How easy it is to catch a virus when my IP address is exposed?

Question

like during instant messaging, the person i chat with is capable of seeing my IP address.

Answer 1

It does not matter whether they can see it or not, the connection is all that is needed.

Answer 2

Very easy, also they do not just need your IP address to infect your pc with a virus. You need anti virus software, a spam blocker, and a firewall.  These usually come in one software package.

Answer 3

If you didn't have virus protection, spyware protection, or firewall protection it can be done easily since MS has as default Well Known Ports open.  

If you are behind a router with NAT and you have a software firewall like the default one with XP or Vista and you have virus and spyware protection software enabled, it could be just a little more difficult.

It's never impossible though unless you are not connected to the internet.