Is there any way to see a sample, either as JPEG frames or as an attached video file of some kind? That would help for the specific questions.
As far as "general advice", there are a few filters I always look to first:
- Levels - tweak images just slightly, as needed, if needed
- Hue/Saturation/Intensity - maybe increase/decrease saturation, tweak as needed, if needed
- Temporal Cleaner - the default settings are way too strong, drop all the numbers on the left by half (30,10,4 = 15,5,2) and drop the numbers on the right by half and then ~half again (16,8 = 5,2) -- increasing these values will remove more noise, but can also add ghosting and chroma trails
Most VirtualDub filters are very task specific, created for one singular task. This is preferred anyway, as those generic "noise reduction" tickboxes in software often do both harm and good, a random mishmash of algorithms.
The filter you need is largely determined by the video you have.
For deblocking video, look to a mix of MSU Deblock and one of the static noise filters (there are several to try). I also own the commercial software NeatVideo, and use it as a VirtualDub plugin -- it's good for this task, too.
Sharpen tends to add noise and severe aliasing, so I rarely use it. It's a really crappy edge correction -- far inferior to a detailer or the Sharpness slider on a Panasonic AG-1980 VCR.
Brightness/contrast is also somewhere inferior to Levels. A bit harsh, whereas Levels is a bit more nuanced.
After you've filtered a video, and output it as an AVI (either uncompressed or as lossless HuffYUV compression), you'll have to re-encode it to an MPEG -- be sure to use good settings in the MPEG encoder, or you'll just re-introduce all the mess you fixed. After it's an MPEG file, re-author to DVD-Video format (with or without menus), and then "burn" to a file in ImgBurn to create the new ISO. ImgBurn can also burn the ISO to a new DVD.
Slow to answer questions last few days. Getting to them one by one.