Search engine (google and live) and Windows Update problem

Hey all!
I've recently come across a problem which has all of these effects:
- When search result links are clicked in live and google search engines (FF and IE) a new browser window opens which displays the correct website (the one the link is to) for a very short period, then 99% of the time redirects to a completely different website. The most common websites it redirects to are smartbizsearch.com and myspace.com profile settings. This problem is also account related; when I log onto a different account on this computer, google and live act normally.

- Windows Update (update.windows.com) doesn't work on any account at all, however it works on a different pc in the house.

- kaspersky internet security (7.0) cannot update - it says that its update files are corrupt. Again, other pcs in the house which also use Kaspersky can update perfectly fine.

- When start menu buttons are hovered over they show a windows Classic green background instead of the usual XP blue (all accounts and new accounts).

- Firefox's start page (http://www.google.co.uk/firefox?client=firefox-a&rls=org.mozilla:en-GB:official) won't open - it complains about a redirect loop. All of the browsers settings are the defaults.

- The minimise, restore and close buttons of all application windows are wierdly larger than normal on all accounts, and the white text in the top right of all application windows is in a different font to normal - I'm not too sure what font it is. (when new accounts are created both of these are still the same)

All of this started happening about 6 weeks ago - We've tried doing loads of things but the problems won't budge Any ideas would be really appreciated!

Thankyou very much for reading all of this - I know its a lot to take in, and I hope it's in enough detail
All the best,
Luke Briggs