to say a pentium 4 is not specific enough
Sure it is
once you've choosend a cpu then you pick out the motherboard based on socket, FSB, ETC.
Well the CPU would determine all that
Do not go 4 a pentium 4, they cost to much.
P4Es cost the same if not less than A64(S939s)
A decent CPu is an AMD Athlon 64 3000+ Socket 754, inc VAT £105.69
And without OCing the P4 will damn near at that alive.
I have a duel motherboard, running 2 AMD 64 3800+ processors 3000MB DDR RAM! N 400GB hdd!!!
It helps your credibility if you dont talk smack. There arent any S939 SMP boards available. Furthermore, do you have any idea how difficult/awkward it would be to have 3000MB??
Firstly AMD64 chips have been proven to run buisness type crap such as autocad much better then the old but isn't Intel still the recommended chip for such things?
All that "proving" stuff is benchmark crap that mostly focuses on the top end chips which are really not cost effective for average users
Not to single anyone here out and I certainly dont want to start anything but you meant 300MB right?
That would be slightly difficult too .... especially considering the smallest DDR memory stick is 32MB and those have been discontinued for several years now.
Now to finally provide a useful answer

Here's a somewhat affordable configuration(s)
Socket775
- P4E-3.20 (S775)
- ASUS P5P800 (i865) or MSI 915P
- 1GB PC3200 (2x512)
- 1 x WD Raptor 36.7GB
- 2 x WD 250GB SATA
- <brandname> PSU, 420W-550W
Should be able to nail that for under $1000
Socket478
- P4C-3.20 (S478)
- ASUS P4C800-E Deluxe
- 1GB PC3200 (2x512)
- 1 x WD Raptor 36.7GB
- 2 x WD 250GB SATA
- <brandname> PSU, 420W-550W
Should be able to nail that for about $1000
The difference between the two?
- The first system allows you to upgrade easily (from a financial perspective) to a PCI-x, DDR2 platform by simply buying a the video card and the memory (if you get the 915/925 based board). Also, the first system doesnt have massive heat issues which the Socket478 prescotts had.
- Now if you have no particular use for PCI-x then its not really really worth this route since (a) the P4Es are clock-for-clock, less efficient than the P4Cs, (b) DDR2 doesnt offer an earth shattering amount of performance -- yet
- The second system gives you a rock solid, proven platform which runs on the much more efficient P4C-3.20 chip and the flagship motherboard.
- if it was me, Id prolly take the second system
But before we can spec the video card there needs to be a minor issue that needs to be addressed:
It will have to handle video pretty good since moslty it will be used as a flight simulator(gaming).Also it will be used in CAD aplications
Pick one. Video gaming and serious CAD work are mutually exclusive (unless you are only doing light CAD work). Why? Because gaming cards are designed for sheer speed rather than pixel precision -- with CAD work, pixel precision is king and as such, a top notch gaming card would be a major bottleneck on your CAD work. On the flipside, a (true) CAD card is designed for utmost pixel precision -- and not for capatability with DirectX or OpenGL (and often dont work or work well with those). There are "halfbreed" cards like some of the low-end CAD cards by ATi and nVidia (since neither company makes serious CAD cards) that can do good cad and semi-good gaming. Thats a choice youll have to make before the VC can be spec'd