I agree with Andraz, forget the Sudan way. Even if you managed to get through the border (highly unlikley) I think you would not be secure in Darfur region. I was there in February and things were already not 100% kosher. There was lots of military activity and tanks guarding entrances and exits to towns, various machine gun emplacements along minor roads and also lots of technicals (Landcruiser pickups with mounted machine guns) cruising around. As recently as 4 days ago the government was supposedly doing aerial bombardments in Darfur.
If you are keen on getting through though and not too skittish you could go to Chad (no problems, get the visa in Abuja in one day, while there enquire about Sudan at the very professional Sudanese embassy in Abuja) and then you head south from Ndjamena to Kome and then on into CAR. I think this should be quiet now, they had a coup a few months ago. From there you could then either load onto a ferry straight in Bangui onto the river Bangui (may have to wait for a week or two), or alternatively keep driving south into DRC, past Gbadolite and head for Bumba or Lisala. With a one or two week wait over there you will be able to get a ferry to take you all the way to Kinshasa, or alternatively east, to Kisangani, and from there you should be able to drive east to Bukavu/Rwandan border. Sounds scary, but is feasible. I did it recently, the other way, coming from Rwanda and then to Kisangani and from there by ferry to Kinshasa. Everything north of Bumba, i.e the stretch from CAR down to the river Congo is controlled by the MLC who I have found a reasonably disciplined bunch. I think if you have some African travelling experience and you speak some french you will be OK.
Regards and let me know how it goes,