Ah - yeah, that hardware can be more than a bit troublesome.
So what you can try to check is plough through the BIOS and see if you can enable an FDD controller (in some cases that's enough). You may want to google for the particular version you have - I've had issues before where there were other mentions where on the WWW of this or that model having problems with PXE booting.
One important thing is trying to update the BIOS - that can potentially resolve all sorts of issues.
Also - try various drivers, sometimes (we find) that a driver 2 or 3 revs back works fine while a "current" one does not.
Ultimately, you may want to look at WinPE - you may still have the odd driver issue there, but it's comparably far, FAR less messy than DOS and the drivers that vendors provide for it.
Hope this helps some.
LANDesk EMEA Technical Lead.