Think you'll need to go for a 8GB card,
Quickly checking my install, seems like it takes a little above 4.5GB
I'm sure it can be trimmed a LOT, but then it would be a pain to install it, since this is set up with openoffice and everything during initial install.
PS I've had good success with lexar cf cards, more the less NO success on Kingston CF cards(1gb & 2gb card), (e.g file systems getting corrupt, trouble with partitioning and such)
Even though i havent tried i guess Sandisk would work fine.
Surely i'd think kingston would be superior on things like this, but not on CF cards if you ask me.
But i'm interested to check if twinmos cards work fine (They are cheap).
Using CompactFlash cards a lot myself with cheap ebay ide adapters.
My home automation epia system with 1gb lexar has had no issues til now (60days uptime currently)., and my carputer with a 4gb lexar has NO issues. (which boots approx 2 times/day)