You did not mention from where you were starting, but if I were in the DC area, I would take I-66 to I-81, go south to I-77 to I-26 in Columbia, SC and then go to I-95.
The huge high pressure zone out at sea due east of Long Island is likely to remain intact. At this time Monday morning, the high pressure will probably keep Isabel from turning northeast thus moving far away from the US east coast. As SeashoreCM said, you don't want to be part of the crowd trying to move to the west and north away from possible landfall zones, as you would be on I-95.
Simply put, just take I-81, I-77 and I-26 down and you will probably be better served. Thursday and Friday heavy rain could be a factor driving everywhere from North Carolina north.
Good luck and be safe.