I was looking for the big bard of the Tripoli and White Rouge... The crap I got at Home Depot wasnt doing anything.
What I do is... If theres paint on it I bead blast it (I'm lazy) paint remover will probably be even better because it wont leave pits in the metal. Then I use an air tool with a sanding disk on it to smooth down all the big imperfections in it (again, lazy and that goes A LOT faster than hand sanding) then once all that is done, I sand in this order: 80, 120, 180, 220, 320, 400, and 600 on the spots that are most noticable.
After all the hours of sanding, I then use the tripoli compound to remove the scratches, then the white rouge to bring out the shine. I used a drill and buffing wheel to do my valve coves, they have a reflection but they are dull (my drill is only 1200rpm) then I used our bench grinder (i think its 3000rpm?) on my altinator bracket and it came out MUCH nicer but it limits the pieces you can work on. My suggestion would be to get a 2500rpm drill, some 3"-4" buffing wheels (one for each compound) and you should be set. I'm going to be doing my intake and valve covers (again) here shortly so I'll post some pictures once I get them done.
Start with something simple and fairly flat just to get practice then work your way up. It takes a lot of patience for sanding unless you have the right tools. A DA sander will work great on large semi flat surfaces.