pxelinux can chain load the 3com menu (mba.pxe) but the 3com menu will then fail to load a .sys image. Here's a really simple fix to directly load your .sys images from the pxelinux menu. Download winimage free trial is all you need, but it's such a great app I bought it. http://www.winimage.com/download.htm
All you need to do to make the 3com images compatible is simply open them w/ winimage and save as .IMZ (IMA is the same, but not compressed - use IMZ) file. That's it. Somehow this removes some of the proprietary header info (maybe). The downside is that the 3com image editor will not work w/ the image anymore, but you can use winimage which works almost as well.
我把用的2个文件上传,你们帮我看下,谢谢。