Ok Dano right ...

first: I also like the PVR 250 so dont misunderstand ;-) ! But as he wants to avoid again spending money your points are also included when doing captures when using one of his Cards.

1. VirtualVCR or VirtualDub in CaptureMode do have an option to resample the audio stream dynamically so you also there will end up with a perfect in sync capture.

2. You shouldn't apply any filtering on the fly while capturing as you never know the quality which comes to your machine. Vdub also gots an onthefly temp filter but if the temp filtering is still not enough to handle the noise of the source properly afterwards you have to add another for instance temporal filter by using avisynth. And heres the Problem. Two times adding temporal filtering ends up in a "static dots on moving surfaces"-Mess. Thats why I never apply any filtering while capturing ;-)

And If he still wants to apply filtering while capturing he can do that by using the ffvfw or ffdshow filter in VirtualVCR or Vdub. FFvfw for instance gots several codecs including mjpeg, HuffYUV and also Xvid (not recommended cause of 4:2:0 Colorspace) and you also can apply some of the libavcodec filter routines like the HQ3dn filter which works EXCELLENT on noise without that much "static dots on moving surfaces" Artifacts.
The filtering is VERY fast and doesnt consume that much CPU power. I did some tests and its amazing ... but for shure risky as you never know which signal/broadcasting quality comes to your machine ;-)

Theres one problem:
Mpeg also uses YV12 (4:2:0) colorspace like Xvid or Divx and that means half vertical color frequency beside half horizontal color frequency!
Mjpeg or HuffYUV do deliver a YUY2 (4:2:2) Colorspace which gives you at least a FULL vertical color frequency!

Do look here to get some infos on YV12 captures:
http://www.kvcd.net/forum/viewtopic.php?t=9380

So a captured stream is a step BEFORE final encoding and as capts always do never get that much sourcequality like a DVD that YV12 problem is noticable .... especially on red edges etc. (well if you do compare with a YUY2 capture)

I'll add one more point on the PVRs :)
The BT-8x8 based cards DAC is only 8 bits.
I believe the DAC on the 250/350 is 9 or 10 bits, and that makes a hell of a difference ;)
I haven't confirmed this, so I'm not 100% sure.
But the quality I get from the PVR at 12Mpbs is better than the Huffy AVI capture with my WinTV GO (8x8 based). So the chipset does make a difference.

Edit: I must be very tired :x
I mean ADC. NOT DAC :P

-kwag

And the captures I get from my ATI Radeon are really appalling. I made a good choice there.

;)