504 MB of RAM
Are you sure it's not 512 MB RAM, sorry I have no answer for this.
This indicates that computer uses onboard video and that 8MB of system RAM is set as "shared" video memory. In many systems with onboard video, Windows reports system RAM as the total physical RAM installed less the amount set in the BIOS as "shared" video memory. Thus, 512MB minus 8MB = 504MB.
If I'm correct, I think you should access your BIOS and see whether you can increase the amount of "shared" video memory. 8MB may not perform well for the DVD use you're talking about here. I think you need to find out more about this before proceeding with your idea. In other words, do you have onboard video or an add-on video card? If onboard and it's currently set at 8MB, can you increase that? If so, how high can it go?