Found out the problem. Atiumdag.dll is outdated in this install. Replaced it with a newer version and now the game runs fine! Thank you BloodCloak from this thread
[EDIT] This problem may only affect those with radeon cards. Hopefully GoG repackages the game with a newer atiumdag.dll
Thanks for the link to that post! Doing this has enabled me to run the game. Thanks!
Details.. after changing that .dll file...
-double click the D3DPopTB.exe file
-main screen is fine at first, but
-when I exit Tutorial mode, the menu screen is all "rainbow and psychedelic"
-gameplay screen is fine thus far, maxing out at 800x600
All of the previous suggestions below haven't worked...
-reinstalling the game
I did so through the installer, of which that was DL-ed via the GOG downloader program/app
-RC compatibility on the shortcuts and changing them to win98, win95, winXP SP2, and winXP SP3
-changing the shortcuts to point to "<path where Pop3 is installed>\D3DPopTB.exe"
I'm on Win7 Home Premium with SP1
AMD Radeon 6600