Help! I have a virus on my Mac 10.4.9?

Please can someone help me. The internet/ Firefox keeps on closing and im getting a message from a site called: xpantivirus.com telling me that it has detected the following 3:

1) spyware.IEMoster.b/spyware/criticallevel

2) zlob.PornAdvertiser.xplisit/highlevel

3) Trojan.infostealer.Banker.s/Medium level

I haven't been on any unusual site. i can use the internet, but its slow, it only closes down occasionally.

I Have tried to load some free scanners/ tools and antivirus off the net, (virusbarrierX5, clamxav, and others)but theres too much jargon involved and i dont know if theyre comaptible with mac.

please please someone help me... and please make advise jargon free...

Help! I have a virus on my Mac 10.4.9?ducati

http://antivirus.about.com/od/macintoshr...