I will go fairly sensible, yet pretty high end.
video card: you NEED to go ati from what the early hl2 benchmarks show. I suggest a ati 9800 non pro costs 200-250
motherboard
for intel: ABIT IC7-Max3 costs 200-250 sure it is one of the most expensive p4 boards around but it is "the bomb"
http://www.abit-usa.com/products/mb/...es=1&model=130
or for a cheaper less feature packed board ABIT IS7 probaly what i would do to save some cash, considering you dont lose too mcuh speed. cost ~100
http://www.abit-usa.com/products/mb/...ies=1&model=79
for amd:
EPOX 8RDA3+ I have a slightly older model it is pretty good. costs about 110
http://web.epox.com/html/motherboard...DA3plus&lang=1
There are tons of other decent choices though for both amd and intel. basically you will want an amd board based on the nforce 2 chipset or an intel board based on the 865 or 875 chipsets. Other brands worth checking out are MSI, Gigabyte, and Asus
memory: all these boards use dual channel memory system so you should get 2 sticks of matching ram. I would suggest 2 512 sticks.
I would also get fairly fast stuff pc3200 or higher. Get a good brand, corsair, kingston, mushkin...
cpu: All depends on how fast you want to go.
just check pricewatch.com I would say at least a pentium 4 2.4C(make sure it is a c model) or an amd 2500xp
powersupply: i wouldnt go less than 350. and get a decent brand, antec, enermax, sparkle.
hard drive: size or speed. speed 36 gig 10000rpm western digital raptor. it is serial ata, the boards above will support it. this is pretty much the fastest non-scsi drive you can get. of course the cost is higher and you get less space.
or pretty much any 7200rpm drive with teh 8mb cache is pretty good.
sound: all the boards have built on sound. the sound on my board is very good but not all are, I would personally try it out first otherwise check out an audigy 2 or a turtle beach santa cruz or something.
ethernet: all on motherboard.
and if you really want more than this, i can find that for you too. but as it is prices were you are are probaly much higher.
well theres a few ideas..