I use my laptop running MS Streets & Trips or DeLorme Street Atlas along with a USB-connected GPS receiver for navigation. I found a neat way to mount it under way so that it's easily accessible to the driver without blocking sightlines, etc.
The Vectra (and Horizon) has a righthand drivers console that looks like this:
The bottom compartment hinges out to expose the controls for the HWH jacks and front slideouts. Above that there is a shallow drawer that pulls out. I haven't found it very useful as a drawer because things aren't contained very well, but it is mounted on slides and it quite sturdy.
I made up a small wooden shelf that sits on top of this drawer when it's extended. It is made from 1/4" birch veneer plywood and finished with polyurethane varnish. I glued some non-slip matting to the surface:
Here's what the laptop looks like sitting in place:
And here it is open for business. I have a small piece of foam (not shown) that I stick on the top edge of the laptop to cushion it against the console and avoid scratches, etc. to either one:
In this view you can see it in operation. My right hand can easily access the touchpad and keyboard if needed. (In general the only thing I do when driving is zoom in or out, hence the white labels for quick identification on the + and - keys.) There's room to get in and out of the driver's seat without removing it if you fold up the armrest, and the laptop screen can be folded down if needed to access the controls behind it. An unplanned plus is that the shelf does a pretty good job of shock-isolation as well.
Here's a view of the top of the shelf:
Here's the bottom. The non-slip pad here rests on top of the drawer front:
And here's a side view. The front piece (on the right in this pic) is sized to be a snug fit in the gap left by the open drawer. The block in the middle sits just inside the lip of the drawer and keeps it from sliding out:
Since interest has been expressed I've added a diagram below with corresponding measurements. If you want to make this I would recommend working first with corrugated cardboard (as I did when I first made this) to make sure that you're happy with the size, etc.
Start by drawing two rectangles side-by-side, with rectangle 'A' 8 3/4" by 14" and rectangle 'B' 3 3/4" by 9 1/2" as shown below. Measure down 13 1/2" on the side of the 'A' rectangle opposite the 'B' rectangle. The red lines which make up the outside angled edges of the shelf are then drawn as shown from the rectangle corners.
The forward lip is 11/16" thick, including the shelf thickness. This part needs to be a snug fit in the opening left by the open drawer, so you'll want to double-check the fit before glueing everything together. Mine is about 2 1/2" wide, but that measurment isn't critical. The other retainer piece is about 7/16" thick and about 2" wide, but neither of these needs to be exact. Finally, all the outside corners should be rounded slightly.
I hope this description is clear enough and proves useful to folks.