If someone get's my IP adress what can they do with it, can they send my computer some sort of virus or hack in to my computer?
yupps. your ip address is the location of your computer on the net. once the location is known, anything can be done, depending on the skill of the hack-attempter on the other end. that's why we have firewalls and other protection programs. and no, before you ask, there's not any way to really conceal your IP, as it's needed by all the sites and filesharing systems you surf to. proxies can be used, but then all your data is filtered through a third party, meaning they have it recorded and could use it against you. that also means yet another party has been added that gains access to your ip to possibly do damage.
This is the first step.. I hit a well known site just as an example. I'm not a malicious hacker..you can get an application called nmap and run it against your localhost (127.0.0.1) and see if there are any strange ports open... You can send me your ip and I can run a scan against it to see if you are open to the world..but if you do, make sure it's by pm..as will be any results returned.. If you want more info about ports, IP's and security visit http://www.grc.com