Q u o t e: Did you get the expansion with it? It adds quite a few features that make the game better. You should consider getting it before you start playing.
Also, unless you find some people who wants to play through at a normal pace, you should try to play most of it by yourself for the first time. Just make an online character and put a password on your games. You'll probably want help with the second boss. He can be very annoying if you don't grind a lot or use a build made to beat him, which wouldn't be fun for your first time.
Duriel is easy in most cases, on normal anyway. OP, if you want to find out for yourself, then don't read this, but if you want a good tip, then here it is. Get an act 2 merc, prayer or defiance. I usually have prayer (not because it's better for Duriel, defiance is probably best for Duriel). Buy thawing potions and use one on yourself and your merc before heading down to fight Duriel. Also, keep rejuvs stocked (the purple potions) for this fight just in case. Fight Duriel, and get him to stick to your merc. Keep your merc under the effect of thawing potions. The reason for thawing potions is because Duriel does a lot of cold damage, and thawing potions boost cold resist for a short time, making him a lot less damaging. If you're a melee class, especially with a shield, you might be better off taking the hits and drinking the thawing potions instead. Keep close to Duriel as much as you can if you're taking the hits, so he doesn't charge as much. Saving cold resist gear can help for this fight too of course. If you didn't pick up enough thawing potions, or your merc died, go back to town and res the merc/get more potions. Your merc should have at least one piece of 90+ defense armor on for this fight by the way. Easy to get from drops or a vendor.
If you choose to play this online, with other people, on your first time through, you have to be cautious. It's quite common for high levels to pop in and start rushing players. Make sure you pay attention to that if you want to actually play the game, not just get rushed.