MSDE (Desktop engine) is a free restricted version of SQL 2000. It has a number of limitations built into it, one of which is a 5 connection limit. As soon as there are more connections that that, it will throttle performance down.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability