If there are certain viruses that can be spread through limewire on PCs can they affect Macs?

Probably not. Cross-Platform viruses (say Linux and windows) are very rare, and the ones reported are just proof of concepts

One that can run in both mac and pcs is to my knowledge unheard of..

If there are certain viruses that can be spread through limewire on PCs can they affect Macs?abtuvurys 2005

some can, most target windows.

If there are certain viruses that can be spread through limewire on PCs can they affect Macs?antivirus programs

There are lots.
it depends on wat type of comp u have
Cross platform virus are not very frequent. But a mac virus could theoretically spread to other mac user using limewire. There's not a lot of mac viruses out there and theres even less (if any) pc/mac cross platform virus, but since mac become more and more popular, it would surprise me to see something that may uses this mechanism in the future.