I entered Sudan from the southeast (Ethiopia) on January 30, 2009. Here's my experience obtaining paperwork for Sudan. I am riding from south to north, dealing with visas as I go. Ethiopia, Sudan and Egypt were the first countries I've encountered where I couldn't get a visa at the border, so going to embassies a country in advance is new for me.

In Nairobi, I was advised at Jungle Junction to go to Addis Abebe and apply for a 14-day Transit Visa, rather than try to obtain a "tourist visa". I decided to go that route, although a Colombian motorcyclist dealt with both his Ethiopia and Sudan visas in Nairobi, so its not an impossible route. And Nairobi (Jungle Junction) isn't a bad place to hang out while dealing with these issues.

You must get your Ethiopian visa in Nairobi - you can't get it at the border - and you don't want to ever do the Moyale to Isiolo road again! Same if you do the Lake Turkana route (get visa to Ethiopia in Nairobi). You also get a customs paper for the bike in Moyale you turn over when you exit Ethiopia - in addition to your Carnet stamps.

So in Addis, I first went to the Egyptian embassy - required for Sudan to issue the transit visa. The Egyptian Consulate has a sign says "apply morning one day (9 to noon), pick up passport next day from 2 - 4 (or 6) p.m. It took me 7 days (what with a weekend and holiday in there) and cost 135 Shillings - $13.00. I don't know if was because I'm on a US passport - turnabout for the way the US issues visas to Egyptians or what - but most people got them per the sign.

At the Sudan embassy next morning - dropped it off, was told to return in the afternoon and pay $200 USD (or get a polite refusal, I wasn't sure), $150 was for the visa, $50 for the visa registration (application). Next afternoon I had my 14-day transit visa. The visa was good for up to 30 days to leave Ethiopia/enter Sudan, 14 more days to exit at Wadi Halfa.

Crossing the border, I had 3 days to get to Khartoum and register at the "alien registration office" (a state police thing). The office has moved from what my Lonely Planet and Tracks4Africa GPS POI are showing - new coordinates
N 15 35.989'
E 032 31.080'

This is right around the corner from the U.S. Embassy.

You need:
1 passport photo
1 copy Sudan visa page
1 copy your passport photo page
5 Sudan Pounds ($2.50) for stamp #1 (your application stamp)
74 Sudan Pounds ($35.00) for stamp #2 (your passport stamp)
Letter of Sponsorship

As to the "letter of sponsorship" (also called a few other things, i.e. letter of guarantee, letter of endorsement) - this is issued by the place you are staying in Khartoum, which likely has a form letter they can provide with relevant details filled in (I got one from the manager of the Blue Nile Sailing Club where I was camping).

Once completed, you have another stamp in your passport - I assume they check this when you exit - and maybe on the road north of here. There are lots of checkpoints in Sudan - and I had to do two other "registrations" at police points along the way (had to supply my own photos for those as well, so carry several up from Nairobi or down from Cairo).

That's my experience. Your nationality may have different results.

Maybe I'll update with my Wadi Halfa to Asswan experience.

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quastdog
Chiang Mai, Thailand