|Did you do it as a Clean Install?|
Windows 7 cannot properly be installed as an update over Windows XP, it creates all kinds of problems (if it works at all).
In order to install Windows 7 on a machine that had XP on it (after making sure all drivers are available), is to (using the update or install DVD) go to Custom and Format/Partition and delete the operating system's partition, create a new partition and format it to NTSF again. Then install it on the clean partition.
All programs will need to be reinstalled, even if they are on another partition or they will not work.
You have to be a little bit crazy to keep you from going insane.