Go to batlabs.com and check out the programming primer.
If you want to work with conventional non trunking channels only then no problem. There's nothing illegal, immoral, or wrong about that. Just don't transmit where you aren't supposed to.
The XTS uses the same CPS as the astro saber. You will have to buy that from Motorola after establishing a Motorola On Line (MOL) account. Then you will have to sign the license agreement and do the whole dance for them. Once you are allowed to purchase it you get 3 years of upgrades with your subscription. The cost is around $300-$400.
You can find good aftermarket ribless programming cables on ebay for around $40. I have one and it's great.
As for trunking, forget it. Unless you are authorized to be on the system you will risk having the radio remotely disabled by the system admin. Then you are stuck with a doorknob that looks like a radio. You would need the system key to even get that far anway, as the software won't allow you to edit the trunking fields without one in the proper directory.