i just saw a poster for windows xp professional.

can people give links for posters advocating linux that i can stick over
the top of it. something with tux breaking windows or something like
that would be nice.

Well first off where do you live? If you tried that in the US it could be seen as illegal. Espeically since more likely then not the said poster is on private property and therefore you have no right to deface it.

I'm not from america so i think it's ok.
also, it's on a big bulliten board that anyone can put anything on, so i think that i am free to deface it in any way that i please.

While I dislike Microsoft as much as any good Linux geek, I don't think that would be a particularly effective way to promote Linux. That just reinforces the stereotype of Linux users as a bunch disgruntled techno-anarchists.

Far better would be to put a Linux poster next to the Windows poster. It should be something that points out the advantages of Linux and open source rather than just bashing Microsoft.

Microsoft has sealed their own fate with overpriced junk products. Linux will not kill Microsoft: Microsoft is committing suicide. Just focus on advocating Linux, and leave MS to reap what they have sown.