most/all vga boxes sold in game stores are horrible. use the xblaster. it works with any progressive signal (gamecube, xbox, even a few ps2 games,) and gives perfect vga output. it even supports 720p and 1080i. the only problem is that it doesn't display a non-progressive signal at all.
X-Blaster will give you flawless output. The only reason I didn't like it was my Samsung monitor had crappy default color settings and I couldn't stand having my consoles with such lousy color (Correctable in XP by a calibration program... but that's software related and won't adjust for console play.)
Xblaster only works with progressive scan games. If you're looking for a cheap good-looking 480i solution, try Dscaler. There's a card compatibility list on there site (some of which can be had for $50 or less), and the software is open source (and free of course).