MSDE - MS SQL Server 2000 Desktop Engine Limits

Uses up to two processors
2GB maxium of memory used
2GB database size limit
Workload throttle limit of five concurrent tasks or users
Will not run on MS Windows Vista

MS SQL Server 2005 Express Limits

only uses one processor (ignores additional processors)
1GB maxium of memory used
4GB database size limit (can have more than one database of 4GB each)
No workload throttle limit

MS SQL Server 2005 Workgroup Limits

Uses up to three processors.
3GB maxium of memory used.
No database size limit.

MS SQL Server 2005 Standard Limits

Uses up to four processors.
No memory size limit.
No database size limit.

MS Access Database Limits

only uses one processor.
No memory  size limit.
Database size limits:
  Access 2002,2003:
     2GB maximum database size less space need for system objects
     255 fields in a table
     255 characters in a text field
     65,535 characters in a memo field entered through a user interface
     1GB characters in a memo field entered programmatically
  Access XP 2GB maximum database size
  Access 2000 1GB maximum database size

No automatic autosizing after database tables or rows are deleted.