If you want to play the newest video games, edit video, or do 3d animations then you need a top of the line computer. If you do not need to do that then you should consider a budget computer.
Dells have a reputation for having good warranties and good hardware that will not give you problems and for being expensive. Acer's have a reputation of being good budget laptops.
If you do not need your computer to be portable then you should get a desktop - they are about half the price of a laptop and easier to repair/upgrade.
You probably won't use the modem so it does not matter.
1gb of ram is enough to do 3d animations but you will appreciate having at least 2gb.
Preferably the wireless card should be G but it needs to match the wireless router you have. G is backwards compatible so you can't go wrong with it. Also it is best if your wireless card is the same brand as your wireless router but that is tough with laptops because they like to use proprietary cards.
I looked at Dell.com for the same laptop. Everything the same except with 2gb of memory and 120gb hard drive is $935. If they are charging you more than $800 then it is not a good deal.
IMO a $300 warranty on a $600 purchase is not worth it.
Dell has good deals on refurbished computers. If you are going to get a 3 year warenty anyways then I see no reason to not get a refurbished computer and save some money.
www.newegg.com is a good place to shop for computers/parts.