every time you encode from anything to a lossy format (like DV) you lose some quality.
From the CCD of your camera to the tape, it gets encoded. THEN it gets transferred to your pc, but it gets transferred losslessly. What's on the tape gets onto your PC, bit for bit.
From there, it's up to you. If you write it back to tape, it'll be encoded again, and you'll lose some quality. It probably won't be noticeable, but it's unavoidable.
mpeg1 and 2 are lossy codecs. There will be quality loss here, but whether it's noticeable will depend on the footage, the length of the footage, and the bitrate you give the video. This can't be helped either, unfortunately.
Oh, and nope, a capture card won't help at all.
AMD Athlon 1700 (@2200mhz from 1466 sod the noise!) - 768mb pc3200 - 200GB Maxtor - Pioneer 106 - GF4 Ti4200 - twinhan/visionplus pci dvb-t - random pci analogue tv tuner - A7v600-x (to replace the a7n8x-d that died...) - random 17\" CRT
Sony STR-DE425 & Eltax c205s;
xBox w/20GB HDD- executer 2.3b;
xBox - standard;
Konica/Minolta dimage z10 w/2x512mb SD;
A silly amount of Cat-5 and usb cables