Ok, jsut to warn you, this is a pretty bad way of doing it, and im sure there must be far more elegant solutions to this. Also you'll need fred06's ruby, joint push/pull, which you can find here: http://www.sketchucation.com/forums/scf/viewtopic.php?f=153&t=6708
Step 1: draw a circle and push/pull it in to a cylinder (i only used 12 segments to my circle to speed up the process, use more if you want a smoother ramp/cylinder)
http://farm4.static.flickr.com/3040/2427666689_00286a8651.jpg?v=0
Step 2: Turn on hidden geometry (view->hidden geometry)
http://farm3.static.flickr.com/2271/2428479614_3dd928ba04.jpg?v=0
Step 3: Using the line tool, draw a line to connect the hidden lines, also notice that ive stopped the spiral just short of the top of the cylinder.
http://farm4.static.flickr.com/3078/2427667087_d552812b10.jpg
Step 4: Select the spiral and move a copy up.
http://farm4.static.flickr.com/3154/2427667223_359db73038.jpg
Step 5: Using the line tool, close all the faces by drawing a line between the upper and lower spiral, following along the hidden line (note ive turned of hidden geometry for clarity)
http://farm4.static.flickr.com/3044/2428480026_8bcf616f05.jpg
Step 6: Soften all the lines you just drew, this will effectively turn it in to one big face.
http://farm3.static.flickr.com/2362/2427667445_e5900f7f0f.jpg
Step 7: select the face and use fred06's joint push/pull ruby to push/pull the ramp out.
http://farm3.static.flickr.com/2313/2428480250_967c359cd3.jpg