Hi - please help me to find out the reason:

I just bought a new PC specially for editing home taped DV to an DVD:
-Pentium 4 3,2GHz
-512 MB RAM
-NVIDIA PCX 5900
-160Gb SATA 7200 HD (there is up to 100 GB free space on them - data rate test shows read 27084 kb/sec, write 30210 kb/sec)
-Intel 915 MB with built-in fireware

when I connected Sony DCR-TRV18E via fireware and start DV quality capturing - everything wents fine - exluding result - captured avi files has a lot of 'snow (small pixels which randomly shows over the frames - in same tame original material do not have any 'noise' if watched directly - the noise are caming during capturing process) . switching-off 'capture preview' reduces this snow by half but there this 'noise is still'.

I tried several capture software (Nero, Pinnacle, Microsoft) but the result are the same - the process of capturing is not clean.

Any ideas ?
(of course there is some software sitting in baccground - Windows XP SP2, symantec antiviruss, symantec systemworks)