The fact of the matter is that playing a caster in the Baldur's Gate series can be very rewarding. Some are content with melee classes, but spells bring a whole new level of preparation and tactics you can use against encounters.
There are a lot of disadvantages to consider though. Do you like being in the thick of fighting? If so, this is probably not a good route as you'll be doing your best to remain behind your meatshields. Though, if you prefer a more active combat-role where you are micromanaging (running away from beasties and constantly shifting between casting spells and making ranged attacks), it can be a welcome break from just assigning an attack and watching the action for the majority of the time.
Unfortunately, wizards are always going to have low HP. Especially in the Baldur's Gate series where that is one of their biggest flaws. Yet, with careful spell selection and a good retinue of melee characters to watch your back, you can overcome this easily. An example is with spells such as mirror image that while not directly increasing your HP or AC, will be a deciding factor in how you survive encounters. Staying concealed with a % that the enemies will plain miss you, or just saying invisible and subsequently out of harms way is very helpful. You live and die on your party makeup and the spells you choose to utilise. I cannot stress enough however that the challenge can be very rewarding.
Your primary focus (apart from surviving that is) is going to be countering significant threats to the rest of your party - as a low level wizard you're just not going to have enough juice to deal with everything that comes your way, so focus on the big things. The little guys you don't need to worry about, that's what the meele is there for. When you encounter a big threat though, or an enemy spellcaster, your priority is going to be dealing with them. There's a few way to do this: dealing enough damage to eliminate the threat before losses are suffered, countering and stripping spells/protections cast by your enemy to make them vulnerable to your party, buffing and enhancing your party to such a point they have a large enough advantage over the enemy to win. Of course, a combination of those is normally what your average wizard shoots for.
I'll try to keep the spoilers low for anyone that hasn't played this great series. If you play Baldur's Gate 1 though (and I would suggest you do this before BG2), then right from the outset your first priority will be getting to the 'Keep' you are instructed to visit where you can pick up some useful NPC companions, an aforementioned meatshield and a caster that can help out with healing or creature summoning in a pinch. You want to keep your party as close to full at all times possible and keep a good variety of characters in there. Don't worry too much though if you end up with two rogues, you can just have them specialise differently (as is a solution for other repeat classes) and there's no justification for getting rid of a character you have a fondness for.
Stick around that general area and see what little errands you can run here and there. Don't start big, maybe just wander the wilderness in the vicinity until you get your first level. The beginning is the very worst when almost all characters are subject to insta-kills due to a lack of a bleeding system and low HP. If you manage to weather it through though, you'll find that Baldur's Gate as a whole is one of the most richly detailed and immersive RPGs ever. What's more, if you stay as a wizard, I can tell you right now that at the end of your career it'll certainly have been worth those awkward teen-levels when your HP was a measely 3 or 4 points.
Regards,
MultiMasky
(Sorcerer)
.. just take comfort in the fact that you attain god like power by the time you get to the end of BG2..
