Basically it's pretty easy to format a PS2 Memory Card you simply need a nifty little program that the guys over @ ps2newz made: ps2memformat

all you need to do is burn this program to a cd-rom and boot it up in your ps2
note: this requires that you have a modchip installed in your ps2 or use a swap magic cd to be able to boot self recorded cds

after the program has loaded press start, wait up to one minute and boom ... you're done.

why would you even want to format a memory card?

well I bought a 32mb memory card and it got shipped unformatted, so I had to chose to either look for a method to "fix" the card or return it. since I'm impatient I chose the first method and suceeded. also this might work to repair "damaged" memory cards and so on ...

hope it helps somebody.