Just compatability issues you may encounter. I would run the compatability wizard before you upgrade. When you put the CD in it should come up with the option and will tell you what things might not work.
1. Must unload all antivirus software esp. Norton AntiVirus
2. If possible clean boot from the XP CD, but this means backing up all your important files and re-loading programmes. Does give a more stable system.
3. Don't activate until your sure all is working well, you have 30 days to activate.
4. If your hard disk is > 20Gb consider using NTFS file system. But stick to FAT32 generally.
5. XP is a massive improvement over Me