Blue book for that car is waaay under $26,500, don't let the dealer tell you what Blue Book is - go to Edmunds, Pace, and KBB yourself. Dealers use the purposely overinflated NADA book. You should know that book is a scam because it published by the North American Dealers (aka Stealers) Association. The maximum dealer retail on that car is about $24K - $25K. However, the true market value is more like $21K - $23K. Add in another $1K if it's Lexus certified. You can buy a new one for close to what they're asking! It would be without the Nav system, buy you could then just add a Garmin Navigation system at a later date.
But back to the car at hand. If you really want this one, here's what you do. Go in there today and tell them you're ready to buy on the spot. Then, offer them $20K. When they tell you "hell no" or "screw off" or whatever, just explain to them that you got approved for an $18K loan from your bank and you have an additional $2K in cash for the downpayment, so $20K is max you can go. They'll try to offer you financing through them for a higher loan amount, but tell them you only trust your bank and you couldn't afford the higher payments anyway. If they still say no (which they probably will), just politely walk out, but leave your phone number and tell them to call you if they change their mind and that you'll come sign the paperwork immediately if they call to accept your offer. This is the end of the month and they're really gonna want to sell the car. So, you just play it cool. If they don't call you tomorrow, call them around 2pm and tell them you're ready to come pick up the car for $21K because your parents (brother, friend, whoever) agreed to give you $1000 towards the purchase. Ask for the sales mgr if the sales guy still tells you no. Be willing to go up to $22K with the sales mgr (only if you really want the car - say you got another $1000 from your girlfriend). Then, he'll feel like he did his job as a closer by getting another $1000 out of you. $22K should be your final offer, you can easily pick up a nice clean '02 for less than that. Good luck, and let us know how it goes. I've got an '02 with Nav myself and can tell you that it's a great car.