I need to split a component video cable and downconvert one of the splits to (preferably) svideo. Any ideas?

The first company I thought of was Sima, as I've had pretty good luck with them in the past, and they have something that'll do what you want (split a component input in two and convert to S-Video), their 7 Input Audio/Video Component Selector Model VS-712-EX, plus more, but it's $800 retail, so probably not what you're looking for on that end.

Can't you just use 3 Y-adapters on a video output cable? Or is that somehow different than an audio cable?

I may be misreading the site, but this looks like a switcher rather than a splitter ... I actually need the component output split to a component signal and an svideo signal concurrently. And I need 50 of them

That very well might work for the splitting aspect (not sure how lossy that is). I'm also looking at:

http://hallresearch.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=HOS&Product_Code=CSV-3&Category_Code=FEATURED

and

http://www.pacificcable.com/Picture_Page.asp?DataName=9A62

but I still can't figure out how to downconvert it ... Actually, I really just need the signal to get into the computer without spending tons of $, but I don't think there are any "affordable" capture cards with component inputs, so I figured the svideo route would be better. I can't believe how hard it has been to find a downconversion from component to svideo though ...

It is a switcher, but it has two concurrent outputs. Not sure if by split you mean to two or to seven, but it'd do it, just a bunch more stuff you don't need for way more than you probably want to pay.

Google shows a bunch of component splitters.

There's this adapter, but it's listed as discontinued. The problem with the converter is that you could have multiple types of signals running over the component cables. Are you guaranteed to be running only one format? If so, especially if that format's 480i, you're going to have better luck. Try this Google search.

Can't you just use 3 Y-adapters on a video output cable? Or is that somehow different than an audio cable?

Given how many powered distribution amplifiers are out there, I'd say that, at best, it'd be poor quality.

Here you go. Go to Camelot Technologies, click on Products, then Cables. They've got a converter listed there.