I am the original owner of a 2001 Lexus RX300 and currently have 73,000 miles on it and have not changed the 2 drive belts (V belts). Is now a good time to replace them? I do hear a slight high pitch sound coming from them. Also, if these belts brake while driving, what's the impact to the vehicle?

If the P/S belt breaks, you lose PS. If the Alt/A/C belt breaks, well that's self explanatory also. They put very good belts on their cars and they last a LONG time. I personally would use the original equipment belts. If your dealer is honest about not jacking the prices up that are in his book, the belts are quite inexpensive. The dealer can do anything he wants with the prices, he's not bound by the retail prices, and many do add to the retail price- 10-20%. You can order the OEM belts from online sources and know what you're going to pay before you order. I would go to a Toyota dealer and ask for them for a Highlander or Sequoia. They may have a different part # but they will be the correct belt and most likely cheaper than Lexus. They often don't let the parts #'s cross reference from T to L because they know it will cut Lexus out of a lot of parts sales with their higher prices for the same part. Just take your old ones with to compare.