Did you have ani antivirus/spyware installed and up to date before this happened?
If you want to void this stuff, never download any free apps - INCLUDING free anti virus/ malware apps/registry fixers etc etc
Norton Internet Secuity 2011 works well and isnt resource hungry on fairly decent spec PCs
Try and backup any important files before you try and fix this ..onto USB stick etc. and afterwards - run the checks on these files
If it was me btw I'd do that, reinstall the OS from scratch, install Norton , then put all your files back on the PC after checking them.