I've done evil playthroughs in both games and it's certainly possible. I will say that as a general rule, Baldur's Gate 2 gives more options for evil players than BG1 (I'm especially thinking of BG2 Chapter 5) but it's still possible to do it in BG 1. The bounty hunters who come after you are pretty frail. The Flaming Fist are a different matter, however, but I think you can keep them off your back by making sure your rep doesn't fall too low.
Otherwise it's a little inconvenient in terms of having to pay higher prices from items, but still a lot of fun.
One bonus in BG2 is that the evil NPCs are probably the best in the game - although there aren't enough of them to fill a full party. This actually makes it easier, IMHO, because a smaller party means higher levels. BG1 has got some pretty good choices too. There you can actually fill a party of evil NPCs, and then some.
At the risk of spoiling the fun of discovering the NPCs for yourself, I will say that throughout the entire series, evil's options are fairly limited as far as thieves go, so creating a PC with some sort of thief skills added in can be beneficial. The "powergamer's favourite" here is usually a Human Thief dual-classed to whatever else, usually a Mage, at maybe around level 4 when you've got enough experience to disarm most traps and pick most locks. Multi-class options here are pretty great as well, though - a Mage/Thief (or even better, an Illusionist/Thief if you're okay with being a Gnome) and a Cleric/Thief are both pretty remarkable classes that open up some great combinations. A Fighter/Thief is incredibly versatile, being able to fill an abundance of roles, but doesn't hold up too well at higher levels (i.e. mid-late BG2).
Or, of course, you can do what I did and just play as a straight Thief, or with one of the kits.