Mac Pro Tower, randomly hanging convinced its a hardware problem but Apple think otherwise

Two things - if you don't know the basics of a unix shell syntax (having a space in the right place matters, punctuation like / matters) don't do step 2 unless you can afford to re-install everything again - the rm command is unforgiving - delete the wrong file or directory with rm -rf and the mac won't boot. You can be more secure by using the srm command instead of rm and it will slowly shred the files - I use srm -sz -rf instead of rm -rf below to shred once and then zero out (which ends up being two passes and then a delete - plenty secure for my needs and not as slow as the default 35 pass overwrite before the delete)

1. Do make sure the person buying the machine knows what they are getting recovery disks for. It's really nice to make a test account to run all the updates rather than hand them the Snow Leopard disk.

2. Set up your Snow Leopard Mac to add one admin account named test with no password and delete any other accounts using the test account. Reboot into single user mode by holding command + s and type these exactly:

    /sbin/mount -uw /
    cd /var/db
    srm .AppleSetupDone
    cd dslocal/nodes/Default/users
    srm test.plist
    cd /Users
    rm -rf test
    halt

You can now boot the mac to see the setup welcome movie plays and quit the assistant a few steps in using command + q when it starts asking name questions and it will shut down with no account created but all the applications preserved. It will remember your wifi settings, so delete those before starting step 2 or use ethernet/a safe public wifi to run updates if you're worried about that sort of thing.

Retail discs are usually early releases (10.6.0 or 10.6.3) lacking driver support for newer hardware models.

Discs bundled with specific hardware models have full driver support and are usully more recent versions (10.6.5 or 10.6.6) but are also restricted to running on just that model or release series. They also contain install packages for any bundled applications such as iLife or iWork.

In most cases the retail disc should work and you should immediately apply the latest Combo update to add any missing drivers or feature support. If the retail disc gives you any errors you'll need the bundled disc.