What version of After Effects? What operating system?
What output settings are you using?
Give us details (ideally including screenshots) about what you mean by "don't look very good".
I use the after effect cs4
In the output settings i`ve tried a lot , from quicktime to windows media, with no compression or jpeg 2000 or H.263(thatone shows me an error that the size is to big)
Well , everytime I make a video , the reproducer collapse, it looks all bumpy and sometimes even freeze (thats my main concern)
Thank you for your help
If you are rendering without compression, it's likely that your files are simply too big for your hard drive to play them back properly. Try rendering a test file using Quicktime Photo-JPEG codec, or H.264.
And yes, 2GB of RAM is very low for After Effects to work reliably.