Clean it up.  It won't be a huge difference, but it could mean a couple
hundred bucks difference in what they'll give you for it.  You want the
car to make as good of an impression on the salesman as possible.
Don't forget to try talking him up a little, too (use the "trade in
values" on www.kbb.com as a benchmark so you'll know what to expect,
but don't expect to always get that full price for your trade).

As far as this being a good time to deal, if you're in the US,
Feb-April is probably the worst time of the year to do it.  Lots of
people take their income tax returns and use it to make down payments
on new vehicles, creating a seller's market.  If you'll look on
Edmunds.com you'll see that there aren't many rebates being offered
this time of year, and that's why.  Also, salesmen are less likely to
negotiate lower prices when they think someone else might walk on the
lot at any moment and pay more.

If you can, I recommend you save your money and wait until late
December.  I know that the holidays are a busy time and nobody wants
the hassle of buying a car then, but that also makes it the best time
of the year to do it!  In mid-late December, dealers are getting get
squeezed from both sides.  From above, they're often are under pressure
from the manufacturers to meet monthly, as well as yearly, sales goals
while moving all the "old" 2005 models off the lot.  From below,
they're even more desperate for buyers because NOBODY has the extra
money to buy a new car at Christmas.  Except you.  Because you've been
planning this for a year, saving your money and biding your time.  And
now you have them right where you want them.  And they're offering big
rebates to get those cars off the lot ASAP.  Sometimes you can save
$3000+ on a new car, with all the applicable warrantees, etc, just by
buying at Christmas time.  Remember: those salesmen work in a job where
their commissions dry up just as they have to do their Christmas
shopping.  At that time of year, they're thankful for whatever business
they can get.

I'll just throw out some other advice while I'm at it.  Hopefully it
helps, if you hadn't thought of it already.  Always make sure you don't
start discussing a trade until AFTER you've agreed on a price for the
car you're buying-- it's an old salesman's trick to claim they're
giving you a great price for your trade, when really all they're doing
is shaving some money off a gouged price.  One local dealer where I
live advertises $8,000 for any trade, no matter in what the condition--
that's how they can afford to do that.

If you do wait until December, that gives you an extra 9 months to save
for a down payment.  My advice is to look up what your monthly payment
on the new one is going to be (check the going rates on bankrate.com
and other sites, then use the auto loan calculator on there).  When you
see how much you're going to pay, start setting aside that amount of
money each month.  That way, when you do buy the car, you'll have a few
thousand extra to put towards the down payment, which will save you
quite a bit of money each month on your actual payments AND save you
hundreds of dollars in interest over the life of the loan.  Or you can
take that money and put it towards any credit card debt you have-- it
looks good on the credit report to have as low a balance on your
outstanding debts as possible, and that'll save you even more money in
the longrun as long as you don't use those cards again.

Anyway, I hope this stuff helps.  I recommend checking out
www.edmunds.com to look up info on the new (or used) cars you're
interested in.  The reviews are very helpful, especially the customer
reviews that tell you just how well the cars hold up in daily driving.
They've already steered me clear of a few potential lemons.  It's a
great site.

Oh, and one other word of advice: whenever you buy a car and you can
choose between low interest financing or a cash rebate applied towards
the car, go for the rebate.  It saves you a lot of interest, and
usually gives you a lower payment.  And NEVER let them distract you
from talking about the final sale price of the car-- if they shift
tactics to giving you a lower payment without talking about the sale
price, it's usually on a long loan that's going to leave you upside
down and royally hosed.  And for the love of god, don't ever let them
talk you into leasing!  Look at "extended warranty" options with
suspicion, but they're not always a bad deal.

Sorry if I started ranting about stuff you'd never do, man.  I'm just
trying to help.  I see a lot of people bankrupting themselves to drive
nice new cars and it makes me sick.  Especially when they got ripped
off at the bargaining table.

Jeremy