Can you convert your roadie for cross?

Probably not. Most roadbikes simply do not have the clearance for cross tires. And you don't have canti bosses for canti brakes...a must for muddy conditions. BUT...I have heard of people successfully converting a roadie for cross...really depends on your frames ability to take larger tires.

Can you convert a Surly Crosscheck for track?

Absolutely. You can convert almost any bike into a track, fixie, or singlespeed...whatever your desire. The less vertical the rear dropout, the easier. Otherwise you'll need fashion some sort of chain tensioning pulley.

Good luck!!!!!!!!!!!