Ok, first, a little info:

Driver: Windows compiled LPMud 3.2.7
Lib: Uber-hacked Amylarr, also compiled for windows

Problem:
Sprintf() will not actually print anything. It just gives a blank line where the output should be printed. printf() works fine, but it doesnt do what sprintf() does...

Anyone have any ideas?

Amylaar is a driver, not a mudlib.

Your mudlib should not be 'compiled for windows', only the driver is compiled.

It's therefore a little confusing to try to sort out your problems.

sprintf() shouldn't actually print anything - it should produce a formatted string.

eg string mystring = sprintf("The number is %d",10);

If that doesn't clear up the problem, the next step is probably to check whether you have a sefun (simulated external function) for sprintf() within the mudlib, and work out what is going wrong in that.

It seems unlikely that the problem would lie in the driver.