Lets say you deleted a file on your memory card for either ps1, ps2, gamecube or any other system which uses memory cards is there a way that you can restore it?

Doubtful. Once it's gone, it's gone. That's why you should be absolutely sure you want to delete the file.

Ya, you'll just have to play the game again unless you found a way to keep a back up on the computer and know how to transfer it to the computer and back...

although gamefaqs.com has some saves you can download but I think their cheat saves...

this isn't PS2/PS1/etc, but with a PSP+Linux, you can make a backup by doing the following:

(as root)

# mkdir /mnt/psp
# mount /dev/node/of/psp/heer /mnt/psp

(as regular user)
$ dd if="/dev/node/of/psp/heer" of "~/psp.img"
$ chmod 644 psp.img

(and to read/write to your PSP memstick image, if needed, within Linux, do the following (make sure the loopback device is in your kernel, also needs root access)):

# mount -o /path/to/your/home/directory/heer/psp.img /mnt/psp

then you can do whatever you want. (if I messed any of this up, feel free to correct me :)

(you should have the amount of free space needed as per your memory stick though. example: you have a 1GB stick, you'll need 1GB free.)

also, if there's a card reader/writer which reads PS1/PS2/GC/etc memory cards, and it works in Linux, you could probably do this too.

Does anyone here know of if there is a cd that I can back the files up onto just in case if I loose the card or it doesn't work anymore which it should still work if I continue to treat it with care? Also is it true that sometimes files on a memory card get deleted without anyone else or you deleting it or is that impossible to happen? Also is it impossible to have someone hack into your memory card? Does anyone here know the answers to my questions.

Dunno bout the cd part...
but your memory cannot get deleted without deleting it yourself...
and its probably possible to get your memory hacked, that is if someone found a way to get to your system...at least

i dont think there is a cd but i back mine up with another memory card ever since the day i was vacuming by my ps2. I seen a static charge jump from the vacum to the memory card it totally fried the card.

Completely submerge it in water. Sounds crazy, but it worked for me.