Roo has pretty much explained it all, but heres some advice about i do it....
I take many sequence shots, and have found them to fall into two categories in terms of camera settup
1) keep the camera in the same spot... e.g. keep the frame the same
2) move the camera with the subject
however, both are different when it comes to editing.
1) will be easier, the frame / exposure / colour / focus will all be the same. Then simply cut out the rider from each shot, and put them all in the same one, moving them into the correct position using the background (e.g. thorugh they're wheels) as a judge.
2) is harder, the camera may have altered focus, lighting, the frame will likely have rotated slightly. And all these catergories have to be conisdered when editing it together. I would say, practise with the simpler idea (number 1 above) then move onto this one with more experience editing
The Major problem with putting together sequence shots is "the rider overlaps himself", but this comes down to again, your editing experience, and which program you use. With photoshop obviously being the best for the job imo!
heres a couple of links to show you some of my work, and to help you understand the difference between my two categories....
1)
http://www.deviantart.com/view/29214695/ - bmx 360 over a spine in the dark
http://www.deviantart.com/view/28481516/ - trials big stepdown drop
2)
http://www.deviantart.com/view/28481567/ - Trials - gap to drop, with the camera being moved between each shot, then put together so that you can barely notice the joins, if you get what i mean!?
Hope that all makes sense.... and helps maybe
Andy