ssd is give and take, it will give you slightly faster boot up times, the write time is seems to be close to standard drives (i think, i have a laptop drive, so don't take my word for it), they are also more expensive for less capacity, and the biggest issue thay have is writing data to them degrades them, but reading it does not--so some have used a ssd for os, and programs, and all other modifiable data gets written/deleted/read onto a standard hdd.
for motherboards, i really perfer not to give suggestions--this is my opinion on the board you have selected, and only my opinion-- and everuyones got one, so don't just take mine...
motherboard, processor, ram: i have heard good things about the zotac boards in general, and am very slowly planning my next carpc around one(once i feel that i must upgrade-- a couple years away). i am really not a big fan of msi, though i have never used one or plan to use them. the processor is fine, and the memory will be more than adequate, some feel that 2gb ram is too much for a carpc running xp-mostly becuase it can slow down hibernate times--i am personally running 2gb of ram and a intel 945gclf motherboard, and don't really care about shutdown or hibernate times, and have setup my system to shutdown instead of hibernating-- mostly for my gps logging program that doesn't like to go into hibernate.
for the soundcard selection, i would definatly recomend the pci card solution over the usb solution, but am personally using the gigaport hd for all my audio, again, my intel board doesnt play nice with everything and so i had to go for a usb solution after the mo-bo decided it didn't want to boot when the pci sound card was inserted.
i have had problems on and off with the gigaport-- i believe that most of them are user error, but some are equipment faults.
if you choose to go with the gigaport-hd, and are doing it for the asio drivers-- and would like to use it for audio modification, DON'T. the driver and software package that come with it is useless for audio playback/modification for a car audio standpoint. just use the windows drivers, and asio4all. the biggest issue i had is that the asio driver is only a output, so in a Console, becsue it would only accepts 1 asio device, it was forced to use just the output of the gigport, and there were no inputs. this works fine with musicians who use midi devices as a input, but does not allow any computer sounds to be outputed from the sound card(again i might be doing something wrong, if i am, please correct me). i also had some problems after the esi software was installed- after the install, asio4all would no longer recognize the card(it threw a error that said that card was 'beyond logic'), and so i have been forced to use the windows drivers.
i don't know how you are planning to set your audio up, so i will give you a quick rundown of my current setup as of 8-5-09(if you look back on my posts, my audio routing setup seems to change everytime i post).
currently, i am using virtual audio cable to route the computer sounds into a program called asio4all, asio4all then sends the audio to Console, my audio setup program/ vst host (to sum this up, the easiest way possible, Console 'hosts' a bunch of little programs called vst plugins that modify the audio in different ways-you can add a crossover, or 31band eq, or time alignment, or whatever else is needed), after console changes the audio, it sends the audio back to the asio4all, which sends it to my gigaport sound card, which sends it out to the speakers.
wow, long post, sorry, didn't plan to post this much..