1. Hardest step: work up the gumption to start grinding on your receiver.
2. Take Dremel, pop off trigger plate.
3. Take drill, drill out FCG pins.
4. Replace everything with 922r parts.
5. Curse the deity of your choice while trying to install the pin retainer(s) of your choice at awkward angles in cramped quarters.
6. Ta-da!
Seriously, the standard "read this" site is
http://www.cross-conn.com/Saiga_Conversion/index.htm. Don't pay any attention to all the talk of mini-mills, center punches and other "um, maybe I shouldn't do this" stuff - having all that may make the process a bit easier, faster or more convenient but it's easy as heck to do with just a dremel, a file and a drill. I did, and plenty of others here have too.
Replacement parts are basically the FCG, buttstock, pistol grip and nut and a bullet guide. You can replace the handguard if you really want to, to get that "real AK" look, but it adds cost and complexity and is purely cosmetic. The FCG group is the trigger, hammer, etc. and is American-made to comply with 922r parts count requirements. Ditto for the buttstock, pistol grip and pistol grip nut (which holds the pistol grip on). The bullet guide is a glorified piece of cut-in-half pipe and bolted into your receiver just behind the barrel to add the 1/8" of height needed for rounds to feed from standard AK magazines. That's about it.
My parts list was as follows:
AKPGNS | AK pistol grip nut w/ screw - $9.00
FCGG2SH | Tapco G2 FCG single hook - $32.00
AKNYHP | Hole plugs - $1.00
X39RTK | Round trunnion bullet guide kit - $25.00
AKBSNB | AK NATO length stock, black - $49.00
AKHITCH | Hitch pin clips - $0.50
TGHWARE1 | Trigger guard hardware - $1.00
Total of $124 shipped, which ended up being cheaper than ordering parts from several different sites - slightly lower prices, but the shipping would have been more. Dinzag threw in some extra hitch pins, a package of E-clips and a couple extra screws for free - nice guy
I believe I got the pistol grip from Midway or somesuch, for around $25 shipped.
Final result (the Saiga's on the right):