When you start your computer Windows takes a good chunk of RAM to operate, and opening POSER takes another good bite from that 512 MB chip, what I recommend you do is to boost your Virtual memory cache according to the size of your hardrive, ( I think the maximum you can kick it up to is 4090 MB and th Minimum is 3MB) you can do this by going into your system settings.

Ask me a question, and I'll give you an answer.