Please answer all of the following diagnostic questions in a correspondingly-numbered list in your very next reply (no need to quote this post):
1. When (approx. date) did you purchase the computer?
2. What is the full name of your installed anti-virus application or security suite and when (approx. date) does your current subscription expire? What anti-spyware applications (other than Defender) are installed? What third-party firewall (if any)?
3. Has a(nother) Norton application or a McAfee application EVER been installed on the computer?
4. Did a Norton free-trial or a McAfee free-trial [pick one] come preinstalled on the computer when you bought it? (Doesn't matter if you never used or Activated it.)
5a. Are ALL of the following updates listed in View installed updates (not Update History)? 
• KB2621440, KB2665364 & KB2647518
• KB2660465, KB2647516, KB2654428, KB2633874; KB2598479, KB2631813, KB2644615, KB2585542; KB2633171, KB2393802 & KB971029
• KB2544521 or Windows Internet Explorer 9 [<=TELL ME WHICH ONE]
5b. When (exact date) was Windows Vista Service Pack 2 (KB948465) installed according to Update History (this time)? 
6. Is Firefox, Chrome or any other alternate browser installed?
7. Are you in the habit of using "Registry cleaners" (e.g., Registry Mechanic; System Mechanic; RegCure; RegClean Pro; Advanced SystemCare; McAfee QuickClean; AVG PC TuneUp; Norton Registry Cleaner; PCTools Optimiser; SpeedUpMyPC; Advanced System Optimizer; CCleaner)?
8. Have you ever done a Repair Install or a clean install of Vista for any reason?
 Start | Control Panel | Programs and Features | View installed updates (in left-hand menu)
 Start | Control Panel | Windows Update | Update History (in left-hand menu)
I have had no luck installing update KB2641653 other updates since have installed fine however that paticular update keeps failing the error code i am getting is 80071AA7 I have tried installing the update in safe mode with networking but could not open windows update whilst in that mode and i have also tried disabling my firewall to install it ??? some more advice would be greatly appreciated.
I am running Windows vista home premium (32 bit) service pack 2.
Try installing in a clean boot state
How to troubleshoot a problem by performing a clean boot in Windows Vista
The purpose of this is to find out if there are any third party applications or services causing a conflict.
@Sarah & anyone else with a similar problem: To avoid confusion, please begin your own, new thread in the appropriate forum. State your current IE version and full Windows version (e.g., WinXP SP3; WinXP 64-bit SP2; Vista SP2; Vista 64-bit SP2; Win7; Win7 SP1; Win7 64-bit; Win7 64-bit SP1) in your first post. Thank you.
HOW TO begin your own, new thread about your computer & your problem
1. When (exact date, preferably) did you do the clean install of Vista?
2a. Was MSE offered & installed via Windows Update or did you intentionally choose to install it?
2b. In Windows Explorer [WinKey+E], navigate to & right-click on
• C:\Program Files\Microsoft Security Client <=this folder
Select Properties: What is the Created date displayed on the resulting General tab?
3. What anti-virus application was installed before you installed MSE, was your subscription still current, and did you uninstall it before you installed MSE?
4. Has a Norton application or a McAfee application EVER been installed on the computer since you did the clean install of Vista?
5. When (exact date) was Windows Internet Explorer 9 installed accoring to Update History?
Note: If all were well with your computer & IE9 was installed, KB2544521 shouldn't be listed at all in Installed Updates!
6. Which was installed first, Firefox or IE9?
7. Is Firefox or IE9 your default Browser?
When i open internet exporer it comes up as ie9 clearly ive done something special ..
Try the following...
[You may want to print these instructions for offline reference. If a Step says to reboot, reboot! ]
1a. Right-click on the following link to download the Norton Removal Tool, saving it to your desktop: ftp://ftp.symantec.com/public/english_us_canada/removal_tools/Norton_Removal_Tool.exe
1b. Right-click on the following link to download McAfee Consumer Products Removal Tool, saving it to your desktop: http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe
2. Close all open applications (i.e., anything with an icon on the taskbar).
3a. Right-click on the file you saved in #1a above and select Run as Administrator to run the utility. Don't TOUCH your keyboard until the run completes, then reboot.
3b. Right-click on the file you saved in #1b above and select Run as Administrator to run the utility. Don't TOUCH your keyboard until the run completes, then reboot again.
4. IMPORTANT - DON'T SKIP THIS STEP! => Re-assert Internet Explorer as the default Browser in the CUSTOM (<=important!) section of Set Program Access and Computer Defaults.
5a. IMPORTANT - DON'T SKIP THIS STEP! => Open Internet Explorer (only!) to http://support.microsoft.com/kb/910336 [ignore the title & Symptoms].
5b. Dismiss/close the automated troubleshooter pop-up; then...
5c. Run Fix It 50202 in DEFAULT and then AGGRESSIVE modes. 
6. Reboot once more then test by running a manual check for updates & seeing if KB2641653 will install now.
7. Reply to this post with a status report.
At this point, I must pass you on to Microsoft Support for further assistance, Gavin...
Visit the Microsoft Virus Solution and Security Center for resources and tools to keep your PC safe and healthy. If you are having issues with installing the update itself, visit Support for Microsoft Update for resources and tools to keep your PC updated with the latest updates.
Customers in North America (i.e., US & CA) can also obtain instant access to unlimited no-charge email or chat support for security updates (only!) by visiting the following Microsoft website: http://support.microsoft.com/oas/default.aspx?&prid=7552
* Please try a lower page number.
* Please enter only numbers.