I run a Virtual Machine with ISA2006 as my home firewall.
With many VM’s I like to turn off the system pagefile to reduce IO, reduced IO is a good thing for VMs, but you need to manage the VM’s memory closely.
ISA2006 can use MSDE (cut down SQL Server 2005) for logging. You can log to flat files but its easier to query the logs if you log to MSDE.
MSDE, like its big brother SQL Server 2005 likes to use all the memory it can find and out of the box there are no limits placed on MSDE’s memory usage which is kinda bad for a VM. Left to its own devices MSDE will happily crank its memory usage up to around 1.7GB which is quite a lot for just writting a few logs, and it doesn’t seem too keen to reduce its memory usage when it’s finished. If you turn off the page file and MSDE gets hungry then you get "out of system memory" messages and the ISA2006 Firewall service stops.
Its turns out to be a bit of an issue which Microsoft have released a solution for in http://support.microsoft.com/?id=909636.
Following the advice in the article you can limit MSDE’s memory usage down to 512MB which gives a bit more memory predictability to my VM. So now I can safely turn off the pagefile and know I’m not going to get out of memory messages caused by MSDE bloating itself.