The book suggested by Mikkel by Mike Predko is a good one to start with on 8051. I am sure there must be lots of others.

Try a search for the Metalink assembler. It is DOS based and free. I have never used it myself though I have it. I have an assembler that appeared as part of a 8051 assembler course in Elektor some 10 years ago. This is good and with a small menu for Assembling and Downloading. Should be there on my PC somewhere. Let me know if you want it and I can mail it to you.


Raghu