If like me you've tried everything else and your log-in and log-off to XP is still tremendously slow then you might try this little trick. First, if there are any other users on your computer see if they have a similarly long log-in. If they don't the problem might be your roaming profile, which is a folder where XP stores your settings you can access them from anywhere in the network. Since these profiles can get really bloated(as in my case) and are not really necessary unless you log-in from different computers in a large network, you should disable it. Here's how:

1. Right click on My Computer, select the Manage option.

2. From the Management Console, select the Local Users and Groups option.

3. Double-Click on the Users folder that appears on the right panel.

4. Right click on the account with the slow log-in and select Properties.

5. Click on the Profile tab of the Properties Window.

6. Erase(but keep note a not of this) whatever path appears for Profile Path under User Profile and Local Path under Home Folder: LEAVE THESE LINES BLANK.

7. Reboot. Try to log-in into the problematic account, you should see a significant speed-boost, the computer might warn you once or twice that your Roaming Profile is not available, ignore it and it will go away, good luck!

Note:  You also will not have your settings and files that a roaming profile provides across a network.