I reckon that you must go to your nearest computer shop. tell them what you want to do on your computer, tell them you only insist of Linux, and if they don't want to help you, they don't wont your money, go somewhere else,
My friend went to our small market computer shop and it was funny that they use Ubuntu Live CD to check hardware.
Don't even bother to build it yourself if you are afraid. The CPU can be a handful to put in if you have not done it before, and most places does not give a guarantee if you blow the CPU.
Mint 9 is so users friendly that most software will work on the hardware, but with prices so cheap these day's I will go big and run Mint 9 LXDE, it will be superfast
Nvidea 1G GeForce 8800 GT 1GB 256 bit
Intel Core i5
4GB DDRAM DDR3 800 1066 mHZ
256 GIG solid state HDD
Blueray writer
Samsung 22 inch Wide screen LCD
And one last thing, everyone experience different things, go with your gut, you will be glad or you will not be, I like to keep things simple
O yes, with wireless, just don't use wireless usb cards, or so called a win modem, surf the net for a Linux modem and it will work
http://lmgtfy.com/?q=wireless+modems+for+ubuntu
The drivers all comes with Mint,