It acts like an external HD without the enclosure. The kit has a power supply, all the ATA connector plugs, and a USB connector. It has everything an external drive/casing has except the "case".
Here's one. If you Google a bit, you can find others. http://www.virtual-hideout.net/reviews/Vantec_sata_adapter/index.shtml
Here's one that does both IDE and SATA. Also got a great review. http://www.crazypc.com/store/merchant.mvc?Screen=PROD&Product_Code=9545&Category_Code= H
I ordered this generic one (USB 2.0 to SATA/IDE) from Geeks.com for $15 but have not received it yet to test: http://www.geeks.com/details.asp?invtid=2020 At the time I ordered (a couple of days ago) they had a deal where you enter the code "FLATRATE" and shipping for the whole order (no matter how many items) is $2 - not sure if it has expired.
This is a cool tool. The USB won't be as fast as a sata port. I use the following setup. My asus mother board has 2 sata connections, I have 2 sata drives in the box and use casper xp to copy once a week. I have a sata controller card in a pci slot with an internal sata connection and an external sata connection. http://www.newegg.com/Product/Product.asp?Item=N82E16816113001 The internal connection is used for a removable hd that is copied to from the c drive and removed from the machine. http://www.newegg.com/Product/Product.asp?Item=N82E16817122105 I use yet another enclosure drive connected to the external port on the card at times. If you've ever lost a drive with everything on it, you don't mess around with chance anymore.
....................offsite backup with all software etc passwords and activation keys written on a piece of real paper in ink.