When you download a game from the PSN store they all come as eboots. All signing does is convert an ISO to an eboot and signs it so you can use it on OFW. There used to be size constraints when using the old signing methods. IE the ISO had to be no larger than about 750MB. There's been a lot of improvements since then. Now you can sign ISOs as large as 1.3GB. If you have an account at Bitgamer I can send you a link to an up to date tutorial.