Wow if you only have 512 MB of DDR2 RAM on your laptop, you're losing alot of that to Windows, and I imagine you have shared memory for your video card, if it's integrated into the motherboard. So, your OS is using part of that 512 MB, maybe even half of it (I can't remember what Windoze needs), and your video card is using probably most of the rest, not to mention any background apps which might be running.
That's only if you have integrated graphics, which you probably do.
If you can run D|S you should be able to run Poser, but to get any kind of performance you're going to need to get more RAM.