Alan is showing the symptoms of having allowed his database to grow too large. He does need to do what I am about to say as well, just in case his problem is elsewhere. If it isn't he can either put up with FTM or move to another program.
If you have not had problems, great, but you need to put your usage in context, how many individuals you have, how large your database is, how much usage you make of the program each day, in particular how much data you enter each day.
For instance I have 135,347 individuals in my database. I have enough work to keep me going 24/7 for an indefinite period and have been researching in excess of 15 years. I am unable to use any of the several variants of FTM I have on my various computers because of the memory problems and crashing.
I estimate I am about one third of my way through processing the entries from the 1940 census, but if I only had 10,000 individuals I expect I could use FTMM (I now work on Macs principally) or FTM without any major problems as I would not need to use the program much at all.
As an example of the different memory requirements Reunion has been running continuously for 12 hours, substantial amounts of data has been entered and 112.4MB of memory is being used.