None of the above. At best you'll get longer RAM previews if that's your thing. If you already have 1 GB RAM (what I have) and a fast CPU (ditto) you're getting as fast a render as possible. More memory won't help. For long renders, as I suggested in another thread try shutting down and doing a cold reboot. That refreshes resources for Windows and that DOES help in actual tests I've done. Not a lot, but in a large project shaving off maybe 20-30 minutes from a 10 hour+ render helps some.
If your system otherwise seems to be running correctly it sounds like the slowness is more a result of rendering a more complex project. Did you did the render test so you have some yardstick to measure against?
Upper left hand corner link to tutorials. If you haven't visited before you need to register. Once there search under DSE, I think the file is on the second search page.
Just to add a Test Bench result. I did an instore test by doubling the RAM [ .5gb > 1gb ] in a pc. The render test came out the same! - This underlines what Encyclopaedia-Man [ BB <wink> ] says.
"Encyclopaedia-Man" - Love it . . .love it . . love it!!!
If you want to see what's happening inside your ram, download a simple little freeware utility called "Rampage." It installs into your system tray, and shows a number representing how much of your total ram is currently not being used.
I have found that Vegas very, very, rarely needs more than 256MB. Even with additional processes running in XP, I almost never run into limits with 384MB. With 512MB, I can have 3 instances of Vegas running (two in the background doing renders at idle priority, one in the foreground for editing) without causing disk thrashing.
In the same vain if you have XP you can bring up Task Manger and it in "real time" it will display a whole bunch of information about how you system is running. Don't be afraid to add to the options shown. The default is rather limited. Under the Processes tab, click on view then mess around by adding other columns.