On weekdays, you should be able to pretty much walk onto anything. Haunted Mansion Holiday Haunt will be up and running--it seems to begin just before Halloween and runs through Christmas Vactation. It's A Small World will probably be closed due to them converting it to Christmas themed (actually a cool way to ride this ride). Unfortunately the Christmas Small World doesn't open until Thanksgiving.
Weekends will have much larger crowds, but it shouldn't be too bad unless Disneyland is hosting some special event. I went on a random March Saturday this last year and they had an All-State Cheerleading competition going which had the parks filled with cheerleaders.
Also, since it's off season, expect something to be down for rennovation. I know Space Mountain is down until 2005. You might want to check with Disneyland Resort info lines to see if anything else will be down--if, of course, that matters to you.
Have a great trip.
