The first result for NASM on Google is "NASM, The Netwide Assembler, Official Site. Latest news, sources, builds. Developers CVS access. Latest version: 0.98.38. ... Welcome to NASM home! ... ". Exactly what I was talking about.
Anyway, try compiling with "nasmw tmap.nas -f win32 -o tmap.obj". I just figured that out after looking at the program's built-in help for a couple minutes (run "nasmw," it says to type "nasmw -h" for help, I did that to learn about the -f and -o, and I found out I should use the win32 format with "nasmw -hf"). So it's not really really hard.
If you're using VC++, it should automatically compile for you as long as it can find nasmw.exe. Try copying that exe to C:\Windows or equivalent.