Let's keep it here, instead of both here & via PM? It's easier!!

The only official site for downloading of LW is www.limewire.com ...you were scammed.
You should contact your CC company & report it, ask them to cancel your transaction. They'll be able to tell you whether or not to cancel your card.
Have a read through the thread below (page 5 has a list of scam sites)
http://www.gnutellaforums.com/showthread.php?t=28751

Providing your CC company can deal with things for you, you may not need to contact the scammers. Just in case though, this thread has advice about getting refunds
http://www.gnutellaforums.com/showthread.php?t=44499

If you've got malware problems, make sure to run an AV scan. Scanning with Spybot &/or Ad-Aware won't hurt, if you have them

If you do decide to have another try with the official (clean) LW...go for the free basic first, from the site I mentioned before.
Keep your AV program updated & scan all downloaded files with that before opening. There are a lot of viruses out there & LW can't control what's shared.