When you switch between Access XP and Access 2003 a windows installer message will appear and you have to wait a long time for it to finally switch.
You can avoid this problem by creating two .reg files — one that you run before you switch to XP, and one that you run before you switch to 2003:
AccessXP.reg:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\Excel]
"win32"="C:\\Program Files\\Microsoft Office\\OFFICE10\\msaexp30.dll"
Access2003.reg:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\Excel]
"win32"="C:\\Program Files\\Microsoft Office\\OFFICE11\\msaexp30.dll"
To make it easy to switch between the two, drag shortcuts to these two files to your quick launch bar.