you can either do it the risky way (you might have to reinstall the other partition if it goes wrong, or the easy, but slightly messy way. ill tell you the easy way as it can be undone again if its done incorrect :D go to start>run and type "msconfig" and hit enter. then, on the "boot.ini" tab of the window that opens, you need to click on the line which corisponds to the option you chose when you boot (so if you select the top OS from the menu on startup, select the top one here)... it will begin something like "multi(0)disk(0)rdisk(0)partition(1)windows="Microsoft Windows XP Professional" /fastdetect"... then click on set as default. change the timout box to 5 seconds, and reboot. if that works correctly, and it boots windows fine, go back to that and change the timout to 0 sec. if it doesnt boot, quickly change the OS to boot from on the menu on startup, go back to the MSCONFIG and change the default to the other one... you could also try the "check all boot paths" button on the boot.ini tab, and see if it will remove the incorect entry. (i havnt used that before so i dont know) hope that makes some sence, im not quite awake so my wording may be a bit confusing!