So what weight would you recommend to a beginner of P90x? Currently, all I have at my disposal is 5 lb weights. I can easily buy different ones, but that's all I have. Would that be fine for a beginner or would higher weights be a better idea?
5lb is too light. I'm sure you can already do a huge number of reps with 5lb weights so that's not going to provide enough resistance. I wouldn't buy fixed weight dumbbells for home use, get an adjustable dumbbell set like this: http://www.walmart.com/ip/CAP-Barbel...-Case/11089974
Then just buy more plates. You can probably find dumbbells and plates for cheap at Craigslist or garage sales in your area so check those out too.