for interfaces I see : ATA-6 , SATA 1.5 GB , and SATA 3GB I'm assuming mine uses the ATA-6 ?
can someone recomend a decent one for less than $75 ??
It is actually sata 150 MB/s and 300 MB/s, not GB. You will never achieve 150MB/s read or write speed on ANY 2.5" SATA drive (and quite possibly only on very few server SCSI 15000 rpm drivers, and only for read), so don't worry about that. Phoning Dell tech support with your service tag will be helpful as they will be able to tell you the interface you should look for.
A couple of things. I just upgraded from 5400 to 7200 rpm on my XPS and I have noticed a very significant improvement in performance, no difference in HD temps, a bit (tiny bit) more noise, and maybe 2-3% lower battery life. IMO, any computer benefits from a faster HD, especially on an OS like Windows (whatever version) which likes to pull from HD often. I listened to the suggestions from some mods here to go 7200 when replacing, and I am quite happy I did now!
On the other hand, your HD now has a plastic piece (proprietary dell) - based on my experience with my XPS - which can not be purchased on its own, but is compatible with any 2.5" HD. Make sure you put this on the new HD so that everything is flush and so that you can pull the new HD out in case of need. There is a possibility that your model doesn't have this though.
You should be able to install windows from any Win OEM installation disc and with your serial numbers on the bottom of your laptop. If you can not, I am positive Dell will send you a replacement CD with little or no cost to you.
I also suggest running from used HDs like from the plague. A great high-end 320Gb 7200rpm 2.5" laptop HD will not set you back more than 70 bucks or so.
For the WD fan, I've had two WD Scorpio's Blue die on me in this laptop. I am a fan of WD Raptors on my desktops since the first one, and I've had no problems there. In my laptops I've never been so lucky with WD so I am currently on Seagate. YMMV, so no universal truth to be said here.