Windows 2008 SBS Memory / Server Issues

I have a client with a server with the following configuration:
Xeon Processor
8GB RAM
2 x 1GB SATA drives
Windows 2008 Small Business Server (64)
Use Exchange 2007
Symantec Endpoint Protection 12.0 small business
Information Foundation Mail Security For Microsoft Exchange (latest)
CA ArcServe for Small Business Server 2008 (latest)

Problem:
We have been seeing very high memory usage on the server for the past 3 months (beginning of the year) in the 90% of phyiscal memory. Seems to be sqlserver (1.2GB), but it goes up and down. There are multiple Symantec process running with the same name (like 7 or 8) that are 64MB or there abouts. The CPU usage is fine.

The server has had 2 events in the past month both dealing with users retrieving files and needing to do a restart to resolve.

First
It was caught early in the AM the first time the server was VERY slow to shutdown, but did shutdown and reboot.

Interim
I noticed the memory was back at 90 to 95 percent utilization and did a shutdown (even though all was working fine.) Stopping Group Policy seemed to take forever to stop. The server was rebooted an the memory was at 55% for about a day or two then went up into the 80s.

Last
The second major event was this past weekend. This time memory was at 95%, the backup Crashed and it started to give an error that a ini file associated with Group Policy was not found. I was able to login, which was very slow to log in. Email was working fine, could see files and folders, but when we opened them MS office would give a blank screen or error. I also could not get the desktop to work well enough to get it to shutdown and simply had to do a hard reboot. There was lots of disk activity.

After the reboot, the system seemed to be fine and the memory was creeping up and was at 70% after about 1 hour. Today, about 24 hours later, it is at 90%.

I have a schedule maint on Tuesday AM and wanted to know what I could do to resolve or toubleshoot the problem. The client is getting frustrated with Windows 2008 SBS.

Thanks