AMD SEMPRON 64 LE-1250 1600FSB 512K AM2 agrh... this sounds very bad imo, basically the processor is your main weapon in VST music making, don't go easy on this one. I would recommend the "Intel Core2Duo E6300" or similar, it is a great overclocker (can get almost 100% performance gain, default is 1.86ghz but i'm running mine on ~3.2ghz on very safe 40-42 celsius) and very cheap, plus the dual core can additionally improve your performance on many applications and VSTi-s.
MSI K9A2GM-F V3 A740G AM2+ MATX DDR2 Onboard Radeon HD2100, 8CH HD Audio, GBE, 16x PCIe, 1x PCIe, 2PCI, 2DDR2, SATA2 i wouldn't recommend any MSI product, they are the most cheapest on the market but i had enough bad experience with them. Try to aim for a nice Abit or Asus motherboard (mine is asus p5b deluxe). Also i don't recommend any onboard sound or graphic card, they will usually decrease your overall system performance, they are unflexible and very bad quality (you could experience some noise cracklings on your speakers while there is a HDD/Processor activity and similar annoying stuff).
Get a decent sound card as the others recommended before me, and get a very cheap PCI express graphic card, since you're not planning to work with graphic anyway.
240PIN 1GB DDR2 800MHZ KINGSTON I would say, 1GB is
not enough nowdays, i'm almost filling my 2GB up with those heavy VST instances, so go for 2GB if you can. 800MHZ should be ok.
80GB WESTERN DIGITAL SATA-II 7.2K RPM 8M - it's allright, you can extend any time you'll have more money/need for additional space.
LITEON DVDRW 20X DL IDE B/W BZL - anything is fine, you basically won't use it nowdays, maybe for some really occasional DVD reading. You see, everything is "pendrive" now =)
KEYBOARD LABTEC STANDARD PLUS alright
LOGITECH BF90 OPTICAL SCRL MOUSE PS2 OEM alright
ENLIGHT 2409 MATX 300 WATT it should b alright
WINDOWS XP HOME EDITION SP3 OEM alright
What makes a good soundcard? What specs you think i should look for?
IMO, if you are focusing on VSTi, almost any decent (30-50$) sound card will do. The whole audio generating process is handled by the processor/applications, the soundcard is basically "unused" here. If you are planning to work with real instruments or use external sound recording, work with samples or similar sound input/output through your sound card, only then should you aim for a "more expensive/quality" card.