Set max server memory, unless you like SQL being able to starve the OS and sitting in a near-constant grow memory, release memory cycle.
At 5 GB of memory total, you probably want SQL's max server memory no higher than 4GB to give the OS enough space.
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