Vue 6 esprit on an AMD X2 4400 w/ 2GB RAM.

I just created 3 groups of 20 objects with no problems at all and have created larger groups of trees when creating complex renders without any trouble at all. I also just tried rendering at 4000x3000 with user settings (46% quality) as a test and that was fine too. So it looks like its a localized problem with either your installation or your system.

Have you checked your RAM for errors with Memtest? Also, what OS are you using? Anything less than Win64 can only access 2GB of RAM so unless you are using a 64bit OS and the 64bit version of Vue then the extra RAM is not being used.