Erasing old computer before the move?

I haven't booted to dos in so long that I can't remember how. Do I press F7 during start-up?

F8, or just hold down the Ctrl key during startup and you should go to the Windows boot menu from which you can then choose the "Command prompt only" option.   (Not sure if this still works on the newest versions.)   On pre-XP Windows there's also an option to reboot to DOS on the shutdown menu.

If you're going to reformat drive C though, I'd be inclined to boot from a floppy which contains the appropriate system programs that you'll need.   If you boot from C, the DOS path settings etc. will all be pointing to directories/files on the hard disk.  Depending upon how much memory is available, configuration settings, Windows/Format version and so on, the DOS kernel may need to reload the command processor (COMMAND.COM) when the format is finished.   Of course, it won't be able to find it, since you've just wiped the disk, so the system will then grind to a halt -- Mission accomplished as far as formatting the disk is concerned, but you'd then need to reboot from another drive to do anything else anyway.

how would you then put on the basic programs if you wished to donate that as well? 

Reinstall Windows from the master CD, then reinstall the required programs.  (May be a violation of copyrights, of course.......)

The thing works soooo slow and buggy, it's not a good machine.

That's most likely not a problem with the hardware but due to the fact that Windows gets so bogged down with junk after a while that things start taking a long time to execute.   A fresh installation from scratch can work wonders on a Windows system which has been running for a couple of years or more.     

groovy_yank, don't let anyone muddy the waters with jargon. If I'm understanding you correctly, you're wanting to trash your desktop PC but you want to ensure no-one will have access to your personal data stored on your HD.  You do not want to donate your PC but you want to trash it and you want to be confident your personal information no longer exists on the HD.  You want to "erase" your HD before disposal thus ensuring your personal data such as pin numbers, credit card numbers, etc cannot be accessed by some random criminal bent on assuming your identity.

Unfortunately, deleting files will only delete the index, the files are still there.  Reformatting your HD does not guarantee all your personal data will be erased.  Using some freeware software will not guarantee your personal data will be erased.  Once data is written to a HD it is there permanently until overwritten correctly  (even if the file index data has been erased) or the media is destroyed.  The fastest and easiest and cheapest way to render your HD unreadable is to disassemble it and pulverize it with a hammer, or rock, or any other heavy and hard object (unless you want to invest several hundered dollars (£'s) in a degaussing coil).
 
Really, it's easy.

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so we had a friend over last night who is in IT and he took my hard drive out-HOW EASY!!!!

I got one of those docks or whatever they are that will transfer the data on there via usb to another computer so i didn't lose the files....

he said my issue must be the mother board!

Cicero:
After doing this, how would you then put on the basic programs if you wished to donate that as well? 

If you still have the software that came with it you just reinstall it again like Paul says. Most places that accept donated computers install their own software anyways.