why get an opteron? you're not doing any overclocking or any gaming are you? why don't you look at a pentium 4 640-660, or if you think you need it, i would recommend a pentium d 950. if anyone says crap about the pentium 4, especially with what it is you're planning on doing on it, don't listen to them, they're just sad no-life amd fans. because i assume you're not doing gaming, you're not going to see any advantage in buying an athlon 64 and definitely not opteron. if you really must buy amd for some obscure reason, then get an X2 4400 or 4800 - which mind you, is much more expensive than the intel 950.
for hard drive, either SATA or SATA2 is fine, because you're likely not going to see any real increases between the two interfaces. western digital and seagate are the two top brands. there is also maxtor and seagate. i personally prefer seagates, because they come with a 5 year warranty, and are marginally cheaper than most of the other brands. the size is up to your preference - 80GB is the bottom of the stack, 250 is the mid-range but certainly more than you'd need, and through to 750GB which is currently the top of the range.
getting a board with integrated graphics will save you the dosh to spend on a better processor, or something else.
on the other hand, i see you're wanting to do some 3d programming, so depending on how visually demanding that will be, the card i'd get would be a 6600GT for good measure.
motherboard is dependent on what cpu you choose to have, get the best chipset possible.
for memory i would recommend Corsair value select range (i don't do generic), in either 1GB or 2GB, whatever is your flavour.
now enermax make great PSUs, as do antec. i would get either Enermax noisetaker 485W, or if you plan on putting in 2 high-end video cards with several hard drives and other devices, the 600W version would give you more headroom for the future if you ever plan on upgrading to SLI or 15HDDs. but honestly i think the 485 noistaker should definitely see you through.