Start with any two identical 'expansions' other than eye of the north (which is a "true" expansion). Basically pick two GW: Prophecies, two Nightfalls, or two Factions.

Based on personal preference, Factions levels to 20 the fastest and for me had the most interesting storyline. Prophecies is the slowest to level, and the little experience I've had with Nightfall I really didn't like the theme and was somewhat jaded over the Dervish class (which had totally ruined our GvG score during Nightfall beta due to massive exploiting of the "Dervway" build)

The cool thing about GW is their targetting and positioning system. If you have a "main" target the thing you want to kill, all the rest of the team needs to do is press "t" then "spacebar" and they will automatically begin auto-attacking the target and they will MOVE the closest path to their max distance where they can attack.

Now, I used to do some hardcore PvP in GW and tell you that unless you're running a spike group in PvP you're going to be kiteable without a true movement system if you use assist and auto-move. I've kited circles around people who don't use click-to-move as a healer because all they did was hit spacebar to auto-run up to me.

Secondly, you're going to need some interesting keybindings for skills and amazing micromanagement to pull everything off, or just use 8 of the same class. In GW, a "long" cooldown is 30 seconds. So start with 2 of the same class, preferably something without adrenaline so I'd go with two casters.

I already have 3 GW: prophecies accounts from my old GW days -- I might have to try this sometime... Best of luck with this!

And no, GW doesn't have any bundled software. Each game is essentially a standalone game that can be attached to other standalones. You'll be extremely gimped in PvP without having all of the GW expansions since your skillset will be limited with just one game. I know certain stores like EB Games near me will offer a few bucks off if you buy 2 guild wars games at the same time, but that's up to the retailer.