Windows administrator accounts has full rights and access to the system and can do tasks such as changing other windows accounts, edit the registry, install programs and so on.. The problem will be if you get infected by spyware/virus in admin account as the harmful programs also will have full access to fuck up your computer. Access to delete system files, install itself as system service and damage windows really bad, you get the point. Its a good idea to have a limited account to use for normal purposes like browsing the net. What I did was just to keep my accounts like it was and then I created a new account. this is how you make a limited account under windows xp.
Click create a new account.
Tick the limited box and click create account.
Now you have a limited account. You can also install applications on the limited account, you will get asked to enter password to an administrator while installing programs so just do like it says and click ok.