When ever I use either MoH Radiant or Wolf Radiant, my computer constanly freezes up, especially when I'm in the middle of changing the size of the brush, actively moving and whatnot. Generally to try and combat it, after every brush i create, i save my map and then reopen it, but this is not always effective. Do i not have enough memory or something? it's a real pain...... i'm really trying to get into mapping, but i've never worked on my map for longer than 5 minutes each time, it freezes so much!!!!
OK... If you have 256+ of RAM you should be fine... However, as Surg has rightly said MOh is memory hungry... If you existing RAM has a problem in the upper reaches then when the Application tries to access it it will crash. But then this would also affect many of your other apps like windows etc.... The other thing is to increase your swap file if you have less that 256mb of RAM..
To test your RAM goto www.freshdevices.com and download diagnose this will tell you if your RAM is buggered and will also check other hardware too.. yadda yadda..