[quote name='mike.m']I had my DC hooked up to VGA long ago, when I saw how crappy my 2D fighters looked, I took it off.

[/QUOTE]
Yeah, not all dreamcast games were designed to take advantage of a vga box. If you check the back of your DC game cases you will see if they have the vga box icon or not.
Of the games I have that are labled as VGA compatible (In no particular order):
Unreal Tournament
NBA 2k1
Time Stalkers
Sonic Shuffle
Skies of Arcadia
Sword of the Berzerk Guts Rage
Crazy Taxi
Ooga Booga
Outtrigger
Aerowings
Daytona USA
Alien Front Online
F355 Challenge Passione Rossa
NFL 2K1
NHL 2K2
Virtua Tennis
Death Crimson OX
Ecco the Dolphin
Shenmue
Illbleed
Jet Grind Radio
Magforce Racing
Maken X
Jojo's Bizarre Adventure
Evolution 2 Far off Promise
Metropolis Street Racer
World Series Baseball 2K2
Marvel Vs Capcom 2
Capcom Vs SNK
Soul Calibur
Heavy Metal Geomatrix
Web Browser 2.0 (it has sega swirl on it so it sort of counts as a game...)
Games that I have that are not labled as VGA compatible (once again not in any particular order):
Sega Rally 2
Shadow Man
Sonic Adventure
Test Drive V-Rally
Legacy of Kain Soul Reaver
Mars Matrix
Armada
Record of Lodoss War
Coaster Works
Midways Greatest Arcade Hits Volume 1
The House of the Dead 2
Fatal Fury Mark of the Wolves
Virtual-On Oratorio Tangram
Dead or Alive 2
Seventh Cross Evolution
Elemental Gimmick Gear