It appears that a _SF_ has been working on a xbox emulator similiar to cxbx

From the readme:

Xeon is an X-Box emulator for the PC. Currently it supports one commercial game, and support for more will be added in the future along with other features.

---------- Compatibility:
Halo (NTSC version only)

---------- Requirements:
Windows XP
DirectX 9.0a
Pentium 3/Athlon XP processor
Recommended graphics card: GeForce FX/Radeon 9200 Pro or higher

---------- Instructions:
Extract all of the files to some directory. You will need an ISO image of the game you want to run. Since ISO reading is not implemented yet, you will need to use a tool such as xISO (www.yursoft.cjb.net) to extract all of the files in the ISO. Make sure to preserve the directory structure inside the ISO file when extracting. Start up Xeon.exe and select File->Load XBE. Navigate to the directory where you extracted the ISO and select the default.xbe file. You can also supply the XBE filename as a command-line argument to Xeon.exe and it will be loaded automatically.

---------- Credits:
caustik for XBE file documentation
Datarescue for their excellent disassembler, IDA

Now, this has yet to be tried and tested extensivly, but a few people have confirmed getting halo to run on their pc with various results (some with full menu's and a few sounds, some with garbled graphics).

Please test this if your pc meets the requirements and give some feedback. You can view the original thread at http://www.ngemu.com/forums and if you dont feel like registering there, you can post at the http://xbox-hq.com forums to give your feedback. Please dont hammer with such questions like "Is this real?", try it out for yourself and see.

Download: here
Download XeonCore.dll: here
News-Source: http://ngemu.com/forums/