I'm looking for a 'slider' (is this the official term?) to fit on the top of my tripod. After some practice, I realize this would be a great accessory. Any recommendations? Is there some way to do it yourself?
Yep, they're called macro sliders or focusing rails. I have the Velbon version. It is all metal, reasonably smooth, and allows both back-and-forth and side-to-side motion. It is also less expensive than most of the other ones out there. The only minor beef I have with it is that the adjustment and locking knobs are too close to each other and to the frame so it can be a pain to operate the knobs.
B&H sells several different varieties - try this link:
Thanks for the infos. I've checked photo.net, velbon website,... and probably found what I was looking for: the bogen/manfrotto 3419. Looks well made, light (480gr), compact and cheaper than velbon ($72 @ B&H). Besides, it's made in EU so I can probably get it for even cheaper here in Belgium.