Buy Dell w/Vista Now or Wait Until Fall for Windows 7?

I'm interested in buying a Dell XPS Studio with 6mb ram, 500GB hard
drive. I plan on using the computer for both work (heavy spreadsheet
and powerpoint), multimedia (mpeg/wmv/flv), Internet surfing, some
games (this is secondary), etc.

Should I wait until September and bypass Vista? Or should I buy one
now, get the one with Vista, and upgrade when Windows 7 is released?

I've never worked with Vista but am very wary of its problems. I use
Windows XP and exclusively Windows 2003 Office. So I'm used to a very
stable environment! But my 4-year old computer (Dell Dimension 4700
with Pentium 4 CPU, 500mb RAM, and 75gb HD) just isn't cutting it any
more. It's really bogging me down.

What say you?