Something is wrong with your system.
FWIW: IE8 is not part of the XP, SP3 install CDs which I have...those CDs install IE7 as part of the default XP install. Which means that the only way anyone can get IE8...is to elect to install it, eithe manually or via automatic updates.
I suggest that you Disable Automatic Restarts When Windows Crashes - http://www.bleepingcomputer.com/forums/t/74644/how-to-disable-automatic-restarts-when-windows-crashes/
. This will enable you to possibly get an error message if the freezing is the result of STOP errors.
Freezing is not a unique occurrence on a system...causes can be software, hardware, O/S problems, and/or malware.
I would check the system for possible overheating, first.
Cases, How to Avoid Overheating - http://www.hardwaresecrets.com/article/142
Cleaning the Interior of your PC - http://www.bleepingcomputer.com/tutorials/cleaning-the-inside-of-your-pc/
Core Temp - http://www.alcpu.com/CoreTemp/
I would also check Event Viewer for errors (not info items or warnings) that might provide clues. I would concern myself with the last five errors listed on all tabs....no point in looking at more than 5 right now. I would also try to check for errors at the time the system evidenced problems.
How To Use Event Viewer - http://www.bleepingcomputer.com/forums/t/40108/how-to-use-event-viewer/