Dell server running Lotus Domino

[VieiraR]

I am running a Dell PowerEdge 4400 for my Lotus Note6 Domino Server. I recently have been experiencing decreased performance. The only thing that was added was a content e-mail filtering program. I did expect some decrease in performnace but not to the extent that is has.
Server:
Processor: 2 Pentium III Xeon 1 Ghz
Memory: 2 256M 133 Mhz
HDD: 2 Ultra3 SCSI Drives 30G 40% used and 4 75% used
OS: Windows 2000 Server
NIC: Intel Pro/1000 Gigabit

Any help or troubleshooting tips would be great.

Thanks,
Rich