Mooash,
When you say 'I'm not allowed to have anything to do with it anymore', I'm assuming that's re: installing new apps on it, or fiddling with the config.
It depends what you mean by remote access;
If you want full remote access, then you'd have to get the go ahead to install VNC (or realvnc) on it, or use the Remote Desktop. If you just want access to the files on it, you could just connect a local share.
For the former, or to be able to browse to the machine, you need to make sure thatyou set XP to access the same workgroup, then you should be able to see it in your network browser, or for direct access, just use an address in Windows explorer for \\1.2.3.4\c$, where 1.2.3.4 is the IP of your parents machine, then login as a valid user. You may also want to set up sharing for any particular areas that you need to get access to the machine (Right-click | Sharing and Security | Share this folder, give it a name). That way you could access the files while your parents are using the machine, provided you didn't hammer it too much.
However, if your post refers to 'NOT ALLOWED ANYWHERE NEAR IT', you'd probably do better negotiating first. ;€)
Rich.