As a side note --
Doing a little research (reading Microsofts 'How ISA was deployed at Redmond' white paper amongst others) suggested that some server tuning was in order.
My home server was returned to Proxy 2, IIS and UT running at between 110 and 120M of RAM used. So it had about 15M of RAM free on average.
Taking Microsofts own suggestion of removing unnecessary services -- Computer Browser, DFS, Distributed Link Tracking, Fax, Licence Logging, Telephony, Spooler and some others that were more specific to my server, this gave back an impressive 20M of RAM.
Taking Johnnyqs suggestion of installing RamIdle worked and it managed to gain back an impressive 30M of RAM.
The bottom line is that after tuning the server I am now running with a whopping 64M of RAM free on average. I have been prodding and poking the server for the past few days to see if I can make it fall over or have to page something back in, and so far I haven't been able to make it so much as blink.
Sometimes throwing RAM at a server isn't the only answer