Forget the power supply included routine unless the case is by a good brand. If you are buying a low cost case the supply that comes with them can quit at any given time. Will this be a gaming case or just the occasional bug hunt?
The X1800XT is right up there with the other high end models out. Some will point at the 7900GT or X1900XT to go with. I haven't heard too much on that brand of memory while Corsair, Crucial, Mushkin, and Kinston get the most reviews. OCZ is labeled the premium brand. For gaming the Sound Blaster X-FI is the one many are going with by Creative Labs. Sound Blaster is noted for the EAX for audio effects while being somewhat resource hungry at times. Diamond is another name. For a look at cards under $40 browse the models at
http://www.newegg.com/Product/ProductList.asp?N=2010360057+4025&Submit=ENE&SubCategory=57
For building guidelines the first things to look at are board mounting in the intended case. You want to make sure the mounts are correctly lined so nothing positive touches ground. The user's manual will become your best friend for connecting the wire harnesses; the one from the power supply and the other for the front of the case itself(power switch, reset, front usb, mic in, usb ports, etc.). Mounting the drives, carefully and evenly inserting video and sound cards, evenly inserting memory, and taking some esd(electro static discharge) precautions helps. Have a good phillips head screwdriver onhand for mounting the hard drive and cd or dvd drives. That will come in handy for a floppy drive if you have one going in.
Assembly of all parts takes time. If you are not planning to use a heat sink/fan combination(HSF) that comes with the processor you will need a good brand thermal compound like Artic Silver 5 for installing an aftermarket cooler there. Another thing is case fans for air circulation to consider. For a gaming case keeping the air inside the case moving and cooled down will see lower board temps. Water cooling and air conditioned cases are not advised for those on a tight budget. 120mm case fans for intake, exhaust, and the side panel are lower cost means of cooling. For other tips and tricks online guides sometimes give you some ideas too.
In addition to beginners articles like the one seen at
http://www.pcstats.com/articleview.cfm?articleID=1444 there are a few building guidelines provided here on this forum. Let's take a look at
First where to buy different hardwares, softwares, etc.,
http://www.computerforum.com/37635-computer-specs-101-a.html
For one building guide depending on type of biuld,
http://www.computerforum.com/16363-building-computers-101-a.html
For technical questions a guideline on what information is usually need at
http://www.computerforum.com/13713-questions-101-a.html
Since you are looking for another case,
http://www.computerforum.com/55610-cases-101-a.html
Of course a sound card needs speakers too.
http://www.computerforum.com/27873-computer-speaker-basics.html
And now the fun begins! Welcome to the Computerforum!