Well, welcome to RO :D

What would be a decent system?
Right now I have several systems:
- a ECS L7S5A2 with athlon XP 2000 and 512Mb DDR(333) and two 80 Gb Seagate Barracuda IV drives
- a Soyo dragon plus with athlon XP 1600 and 512 DDR (266)
- an Abit KT7 Raid with athlon thunderbird 900 MHz

Do I need a raid-system and how big should the harddisk be for recording a 1 hour live-show in highest resolution (16 ch)?

I've seen the Terratec EWS88MT as a soundcard in promo: 299€.
Is this something good?
Which soft should I use for recording?

Well

Quite an articulate question, so it deserves an articulate answer.

System: I'd go with the ECS/XP2000 system that seems the most suitable for a DAW machine; I don't know ECS mobos (is this what ECS refers to isn't it?), but as long as the chipset is compatible with the soundcard and app you decide to use it's no big deal, Opus is certainly more informed on this subject. The rest seems appropriate: 512 Mb of DDR Ram, OK, 2 80Gb Seagate drives (I hope they are at least 7200rpm, whatch out for those I had some bad experiences with Seagate).
You don't need a RAID array, as the newer, faster CPUs and drives can handle large streams of data and 16 channel isn't something a good, well configured DAW machine can't deal with: I can record a full 24 track session at 24bit 48KHz on my Asus Mobo/XP1800 + Digi 001 setup for more than 1 hour without any hiccups.
Some, if any, troubles can arise if you need or want to go at sampling rates higher than 48KHz, say 88.2 or 96: the machine will be a little more under stress, that's where a good CPU and fast drives help.
Drives size also depends on the resolution of the recording: the higer the sampling rate, the more space it will take: a simple CDr holds up to 650Mb and that's a 2 Channel 44.1KHz 16 bit file, if my math is correct a single mono 24 bit 88.2KHz file can go up to 845 Mb (1 hour long); multiply that for the n° of tracks and you should get an approx total of the drive space you need; judging by the drives you have you shouldn't have any space issues.

Soundcard; there's loads to choose from; I don't particulary like Terratec products, I once worked with one and didnn't like it's converters at all; right now my favorite is the MOTU 2408MKIII ( http://www.Motu.com ): lots of I/O (analog and digital) comprehensive sync capabilities, compatibility with just about all of the major audio software, expandable to the user's needs, good converters. Check it out, it's more expensive than the terratec, but it will provide you a professional tool at a reasonable price. Whichever you choose be sure it has the I/O capability you need for your recording: for the gig you are about to start you need at least 16 analog ins to accept signal from the board; if the soundcard you choose only has 8 or less and the rest is digital ins you'll need a separate converter box, or a different soundcard (also form MOTU there's the 24 I/O that has up to 24 analog ins, NO, I don't work for MOTU :D )

Software; as for the soundcard there's lots to choose from and since they almost have the same capabilities it comes down to poersonal preference and ease of use. My favorite is Pro Tools, but it requires it's own hardware and won't run on other soundcards, so for a system like yours I'd suggest Sonic Foundry Vegas or Logic Audio. There's others from Steinberg's Cubase SX or Nuendo to Cakewalk or Samplitude and Cool Edit. Each engineer has his/her favorite so I suggest you check out severeal and download some demos from the manufacturer's web site to find out what you like best; keep in mind your needs: some do audio and MIDI some do only audio, so be sure to look at the features you need.

OK, I hope I 've benn helpful, my last advice is: whatever system you put together be sure TO TEST IT SEVERAL TIMES BEFORE THE LIVE GIG, and make sure it's stable and reliable: there's nothing worse than a crash in the middle of the show and even worse loosing all of the recorded material; each time I do a similar thing I stop the recording in the middle of the applauses every 2 or 3 songs, so I'm sure that the material already recorded it's there no matter what could happen, and applauses can be edited later in post.

Good Luck and post back your results.

:tu: L.G.