Request Info: 1st time visit to CA wine country

[Jodi]

My husband and I are planning a first trip to Northern California for this April, and aren't sure quite where to start. We plan to spend a couple days/nights in either Sonoma or Napa County, stay in a B&B, and tour/taste several vineyards. We are not wine experts, but love wine (typically enjoy Cab. Sauv. & Chardonnay, and avoid spending more than about $10/bottle). We'd appreciate any suggestions about the basics: Napa or Sonoma (and can you stay in one but reasonably "do" both in 2-3 days?)? How many vineyards is it reasonable to visit in one day? Are there certain vineyards that we should try not to miss (e.g., particularly scenic or informative, and/or where we could taste great wines that are not commonly available outside of the area)? Is there a specific area within one of the counties that has a particularly high concentration of vineyards worth visiting? Any specific books or web sites you'd recommend? Thanks in advance for any help!