Dellauction.com: Precision vs. Optiplex

Hi guys, once again I need your vast computer knowledge.

I want to buy a computer on dellauction.com. The reason? Because I can buy one fairly cheap and it will come with XP. The computer, of course, will be "refurbished," which means it was used, and Dell fixed it back up to resell. Of course, I am looking to play Maplestory with the computer.

 Question One.

1. The computers come in two "models," Precision and Optiplex. There seem to be a lot more Optiplexes than Precisions. For someone dumb like me, can you simply explain the difference, or tell me which one I will be wanting?

 Question Two.

2. What "specifications" am I supposed to be looking for, to make my computer good. Not just average/will do the job for bosses. And not godly. But above average/good. Here is an example of what the chart looks like with specs for specific computers:

FAMILY	PRECISION
MODEL	WS390
CHASSIS/FORM FACTOR	TOWER
PROCESSOR	INTEL CORE 2
PROCESSOR SPEED	1.9 GHz
MEMORY	2048 MB
HARD DRIVE	80 GB
NETWORK INTERFACE CARD / ETHERNET PORT	10/100/1000
OPTICAL DRIVE 1	DVDRW /
OPTICAL DRIVE 2
ADD'L STORAGE (ZIP)
OPERATING SYSTEM	WINDOWS XP PRO+
INPUT DEVICE	Keyboard and Mouse
USB PORT	7 USB 2.0 PORTS / No Card Reader
INTEGRATED AUDIO	YES (Speakers not included)
VIDEO RAM	128 MB
CONDITION	Refurbished

If this is not enough information, this page is where I got the specifications, but since it's an auction the page will soon expire.

My friend said don't worry about hard drive because I can just install a TetraBite in it later which is like 1000 GBs, but how can he tell? (, because my 2002 computer now is XP, but only has 256 MB Ram, and "2 slots" for RAM. How do you know this one can fit so much?)

Thanks a lot for the help in advance guys.