Unless you find stuff just "left on the shelf" you may have a hard time finding IDE or EIDE hard drives. They've pretty much disappeared in my local shops.

There still are plenty around online (I rarely visit a shop) in the UK. I'm not sure but out of the 5 PCs here, Pip's might still need IDE drives. The rest have SATA support.

As for disk size. I've been using 160Gb which has been more than enough except for the mythtv server which does have recordings, CDs and DVDs. Got a 750Gb in that.

I've got a spare 750Gb drive at the moment (one was replaced under warranty but I had to get a new drive while waiting for the claim to be processed). I'm toying with putting this in my spare web server box. Currently, this box is woken up once a day and does the web server backups and shuts itself down once done but I might just try to extend its use to back up the other PCs data onto this spare drive.