I'm tired of my Ford Ranger and my 92 Mustang GTconv is too old to be a daily driver. I got divorced and now want a fun car. I drove several different cars and the Z4 was my favorite. I have a nice garage with a lift in it, so I'm ok to take care of my own repairs although I am not a professional mechanic. I'll probably get a low mileage 03 or 04 off ebay for about $20k. I'm looking for a fun car that I can put 150 miles a day on. I will be driving it in the winter, but there's rarely snow on the road here and I can drive the 4wd truck when I need to. I will be keeping it outside. I've read about problems with drain lines. Where are they? Also how hard is it to find a hard top? Are there any real differences between 03 and 05? I read about a cooling system upgrade. What years need that? Anything else I should know? Thanks!

What's the factory warranty on these?

same as all bmw's (4 year/50000)...unless its cpo's..then 6 years...and additonal 50,000)

It's pretty difficult to find a hard top - they weren't a common option since most Z4s are 2nd or 3rd cars and not driven during inclement weather. Do a Google search for a write-up on clearing the top drains, there's a detailed one out there. I think the Z4um one is in the Google archives, and there might be one on www.zpost.com as well. Like most problems, this is greatly inflated on the internet - it actually doesn't happen often as the cars are typically garaged.

There were some small changes from 03-05. The convertible top can be lowered via the key remote starting in 2004 and the headlights and taillights changed a bit in 2005, before changing again in 2006.

As I've mentioned on this forum 2 or 3 times already in other threads, there are some good, detailed buying guides in the current issues of Bimmer (a US magazine) and BMW Car (a UK mag).

Here is the link to the drain plug DIY: http://www.zpost.com/forums/showthread.php?t=63033
I did it last weekend and it took about 2.5hrs. It was a fairly simple process.
Dare I say this, but since you have a lift, a Z3M vert modded would be kinda cool too.