hey guys,
just a short comment. actually this ms_1_exc_disableIfOS="w2k" stuff never worked for me, i got the same error message every time.
what finally let me succeed was that i inserted a semicolon in front of the filenames mentioned by Marco in dosnet.inf (so like ;d1,ahci7xx.sys etc.) and i removed every line which contained these driver names from txtsetup.sif. i mean after slipstreaming. and it actually works this way.