I think you are paranoid about something you don't understand.
Your IP address is useless to someone. IP addresses are used by computers to find other computers on a logical (not geographical) computer network. They are assigned anonymously, at random, on demand. That means they are the computer network equivalent of a prepaid cell phone. You can't possibly know who owns a prepaid cell phone, or even where they're located, simply by knowing the number.
Your IP address is given out everywhere, which is what it was designed for. It's kinda like a call-back number of sorts, which tells the server where to send the requested information back to. It's like giving out your home address when ordering a pizza. Every website, every email, every IM, every download... your computer gives out your IP address to every computer you talk to on a network.
People can dial up and contact your computer either intentionally or completely at random. Your computer doesn't answer the communication firsthand, rather it sends it to what's called a port. Your computer has over 65,000 available ports. If there is a program running on your computer, listening on the port, the program accepts the communication and does whatever it's supposed to do. If there is no program listening on the port, the communication is ignored.
Programs that accept communications must also understand what it's being told. You cannot call up a program and tell it to go ahead and dump your passwords; things don't work that way. Programs that are listening on the network do so for a very specific purpose, such as web serving or instant messaging. The listening program is expecting to be talked to in a specific way, using specific words; this is called a protocol. If a program receives communication that doesn't exactly match it's protocol, it ignores it.
Some Windows programs that run on the network, such as file sharing services and such, contain bugs that may allow an attacker to take control of the service and do bad things. This is called a vulnerability, and the act of using a vulnerability to do something bad is called an exploit. A good percentage of viruses spread and infect by exploiting Windows services.
Microsoft is hard at work every day making sure that any vulnerabilities that are discovered in their software are fixed as soon as possible. These fixes are called patches. Since Microsoft has to have a hip, catchy term for everything, they call each bugfix and/or security patch a "hotfix". These "hotfixes" are downloaded using Windows Update. Needless to say, it's very important you are updating every time it tells you to.
To protect yourself, make sure your Windows Firewall is running. Make sure all of the ports are blocked, except for ones you know you need. Turn UPnP on, so other programs (like Messenger and stuff) can setup port forwarding automatically.
Also, change your account to a limited account. You don't need full admin privileges for everyday computing. Using a limited account means that the programs you run also have limited privileges. This is good if a virus were to be launched under your account: it wouldn't have permissions to change/delete system files, and would simply not work. If a virus were to launch under your fully privileged account, it would have free reign of the system. Create a second limited account if you can't switch to a limited account because you're the only user on the system.
Your "program not responding" messages along with strange, unknown, or randomly-titled programs are a clear indicator of a virus, not a "hacker". Boot into safe-mode-with-networking and do a full system scan. It doesn't matter what antivirus you use. Just pick one a do a scan. Don't install antivirus that will run full-time. It's unnecessary if you are a limited account and your firewall is running.
I don't have an explanation for that Limewire thing... Are you sure you weren't remotely browsing someone else's shared folder — which is perfectly normal? Also, everyone watches porn. Maybe not you or your giggly 15-year-old friends, but everyone else certainly does. Don't be freaked out about it, it shouldn't be "disturbing" in the least bit. You'll understand when you grow up... unless you end up becoming a nun.
Look, you shouldn't have to worry about going through "something bad". You aren't being "hacked". That's not even a correct term. If someone is in fact breaking into your system, the whole idea is to do it so you don't know. You can't detect an intruder unless they do something dumb and make it obvious. If they have the skill and technique to actually break in, you know they won't me making any bone-headed mistakes.
Changing, masking, or altering your IP address in any way won't do you any good. The Internet would still work, wouldn't it? Of course. Communications will still get back to you, and they can only find you if you have an IP address. If you want to be absolutely safe, pull the plug and don't use the ne