I'm currently doing a bit of travelling with my laptop that's basically an I3 core with integrated Intel HD gpu, I'm looking for an MMO that
1: Isn't huge in file size (I have an 800mb daily DL limit before my ISP throttles me to dial-up speeds for the day)
2: PvP friendly
3: Has an RP server but not completely necessary if the community isn't 95% spambots
4: Not blatantly P2W but I'm not against cash shop vanity items or subscription bonuses
5: Active enough to be able to easily find groups
My favorite low spec MMORPGs are Ragnarok Online and Maple Story. RO has quite nice PVP and probably still has people into RP (though there isn't a dedicated server to that). MS maybe doesn't really fit to your requirements, though I heard they added PVP lately.
Last time I checked both where around 3 GB downloads (which is small for today's standards).
Even smaller I can only think of Spiral Knights, but I'm not even sure if that has PVP at all. It's more a Zelda-like coop game with randomly generated dungeons.
Edit: Oh and Nestalgia hehe. But it only had around 30 players last time I checked, better start playing it with 2 friends (it's also solo-able though).
Mu Online- Freaking awesome and if you like fast paced combat go dark knight. They have the sweetest combo skill that just murders <3 gotta be quick on it though! Cash shop is considered "p2w" but if you have time,patience,and some skill you'll be fine and can usually get the items(wings,armor sets,ancients) for around 100-600 jewels. Haven't seen many people role playing(which is a damn shame!) but you might be able to find a group like that on the forums or just make your own. Group finding is fairly simple...if they aren't botting which is legal in the game so it might be a turn off for you. :/
Wakfu- If you liked Final Fantasy Tactics you're going to love this one. The NA version is p2p though with heavy restrictions but this post says that their is a version that is f2p http://www.onrpg.com/boards/threads/...ully-F2P/page2 check it out if you're into it :3
Allods- My pos laptop could handle it so you should be able to run it. f2p/p2p versions are available with the p2p version being more friendly towards those of us that don't wipe our butts with $100's
You could give Tibia a shot, pretty old school and it has pvp server and some RP i think. Haven't played for a long time so i can't tell you much about it nowadays.
You could also try to look for some browser gamers, kongregate.com is full of some neat, fun ones.
I think Dark Ages just went f2p or something like that, it is very low spec and a lot of RP as much as i remember.
You can also try Nexus TK or Illutia.
All of these games are 2d and pretty low on requirements, give them a shot and see for yourself if you get hooked up.