SMG are fun, my last car was an SMG, and I absolutely loved it... but can be very expensive to maintain.. the extended warranty wont cover the pump, which usually goes after 40K... BMW will charge you about 3-5K with a new clutch, and clutch slave. The rebuilt pump cost $350, + $500 in labor at an indy shop tho'. The M series 7 speed SMG are less problematic I hear.
Conversion? nothing is impossible, but its not worth the MONEY... its will never be perfect, you should check out e46fanatic.com alot of info there on the SMG, my friend converted his to a 6speed, and a lot MONEY+TIME spent eventually he sold the car because 1, 3 never worked accordingly.
Check out ebay. I bought my last car from there, I had paid $100 to this company who sent a rep out there and inspected the vehicle... VERY DETAILED INSPECTION, they will give you a PDF with pictures of anything and everything.