To return to Simon's point about focussing, I think Pentax are pretty much on a par with other makes and I doubt that there's any difference between the *istD, DS or DL. The only real difference is the number of AF points and most discerning users switch to center point anyway - thus eliminating the difference!
Multi-point AF systems were developed to speed up the focussing process during rapid fire point and shoot photography. By and large the system works well and ensures a reasonable percentage of accurately focused snapshots, where the photographer doesn't have the time to precisely focus on a certain point and then recompose for the final image.
I personally prefer to set the hyperfocal distance on the lens in use and set the camera to manual for such occasions and leave the camera set to AF single, for more precise work.

Canon have possibly just had the edge over others for some time, due partly because of the floating elements within their 'ultrasonic' lenses, but there's really not much in it and sticking with Pentax would mean that all your current lenses and accessories would be usable.

For an 'auto-everything' lens by any other manufacturer, as long as it's described as "Pentax auto-focus" or words to that effect, that should be fine. If you're happy to consider a manual-focus lens then you're looking for a KA mount ie. with electronic information contacts.

As you know, any K mount lens will fit and function within it's limitations but to get the most out of the camera / lens combination, you really want the KA version - all Pentax dedicated auto-focus lenses are effectively KA.

For genuine Pentax glass, look for F or FA series 35mm film lenses (remember the 1.5x crop/magnification factor) or the DA lenses that are optimized for the digital sensors.

Don't discount the FAJ series (no aperture ring) but they're obviously less flexible for those photographers that appreciate the hands-on approach.

I agree with John - eBay is always worth checking out.
Don't restrict yourself to just looking for a lens though, you'll be surprised at how cheaply you can pick up the lens you want plus a camera body - which if you don't want to keep, you can sell on.
I recently picked up a cracking F 50mm 1.7 at a real bargain price because no one seemed to want the SFXn that came with it. I only really wanted the lens but there's absolutely nothing wrong with the camera and I think of it as an added bonus

Well I guess the answer is 'yes and no'.

A fixed 500mm can be very useful but also somewhat limiting. It's a serious telephoto length and becomes a 750mm on an *ist DSLR, which makes it very tricky for hand-held shots. You'll need a fast shutter speed, plenty of light and preferably a decent tripod.
You asked about a zoom and although I can't recommend a specific model, I would have thought that either a 70-200 (105-300) or 100-300 (150-450) would be more usable and versatile.

There are loads of zooms in the 70-200 ish range that you could pick up quite cheaply to experiment with before investing in a more specific choice.
I'd look for a Pentax A series (manual) or F/FA series (autofocus) zoom - general rule, stick with Pentax

"Fired many shots and didn't kill anything" - except a few squirrels then

That's not very sporting, securing a squirrel in place with duct tape before shooting it

Mac,

something like this http://cgi.ebay.co.uk/Flash-gun-Slave-unit-for-any-flashgun-NEW_W0QQitemZ7572841552QQcategoryZ15221QQrdZ1QQcmdZViewItem would probably do the trick.

I've got a similar device, a little cell with a rubber sucker on the bottom and a short synch lead to connect to either a socket on the second gun or a hot-shoe adapter and I must say it works very well - and it's cheap!

All perfectly understandable Arthur - nothing to be ashamed about

Congratulations and well done that man!

"necessary" - absolutely essential I'd say

Hello Don,

Have you tried the lens on another AF camera - to see if you get focus confirmation?
I presume it works ok at other focusing distances and light levels?

The obvious answer to that question is that your current lenses and most of your accessories will work perfectly with a current Pentax DSLR.
The only real drawback to the APS-C sensor is that moderate 35mm wide-angle lenses of around 28mm focal length, are not really wide-angle at all and you need to go to 18mm in order to get the same angle of coverage.
The flip-side to this is that a standard 50mm becomes a nice 75mm portrait lens and a 100mm effectively becomes a 150mm etc.
Also, the smaller image circle means that you avoid the area covered by the edges of the lens and therefore maximize the optical qualities of the lens - because most lenses are sharper toward the center.