Exchange 2000 memory allocation

I have a problem with an Exchange 2000 server SP 2 that uses all physical memory and a bit more.
It’s a 1 GHz server with 512Mb RAM.
The server is very slow and users are complaining a lot 🙁
Is there any way of controlling how much memory Exchange is allowed to use, like in 5.5 ??

Regards
Mathias Nilsson