This is a working flow that works really well for me now so I thought I'd share the info as
Greg B. is trying to so something similar. I'm sure a lot of you guys are already doing mosaics your own way. This is just another approach and it's bullet proof. So far...
You will need
CCD Stack,
Registar,
Fitsplug from Eddie Trimarchi's astroshed to load FITS in PS and
Photoshop CS5. Haven't tried in CS4 or CS3 but I'd assume the blending/HDR methods are also implemented in these versions.
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CCDStack
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Load panels in CCDStack
Check int mode in background for each panel (select a background area devoid of dark neb or bright stars)
Note value
Pixel math +/- on each frame to match smallest int mode of all the original panels
Set min (background slider) and DDP with plenty of room on the histogram but still visually appealing stretch (i.e. not washed out) If it looks contrasty and good beware you're likely to have clipped data already in the black point.
[Background:50 - DDP:400 or Background:100 - DDP:700] depending on channel is fine
Save all panels as 32bits FITS float - suffix '_32bits float equalized'
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REGISTAR
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Clear registar.ini (blank and save it with notepad)
Load central panel in Registar (set registar not to scale FITS and no noise reduction)
Register all panels to central panel - union
Combine -> max
save combine1.fit
Close registar
Clear registar.ini
Open registar.
Load combine1.fit only.
Register all panels to combine1.fit - union
save all panels as FITS - they get suffixed with '_32bits float equalized_reg'
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CCDStack
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Load all 32bit FITS panels in CCD Stack you've just saved from registar.
Might take a little while.
DO NOT touch any display settings in CCDStack (i.e background, DDP, etc)
Save scaled 16bits FITS unsigned - suffix '_scaled 16bits unsigned'
so all files have now a suffix '_32bits float equalized_reg_scaled 16bits unsigned'
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PHOTOSHOP (CS5)
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For this step you will need
Fitsplug for PS to load and display FITS files like any other bitmap file.
File > Scripts > Load Files into Stack ...
Browse - load all '_32bits float equalized_reg_scaled 16bits unsigned' FITS panels.
Untick 'Attempt to Automatically Align Source Images'
Untick 'Creat Smart Object after Loading Layers'
Click OK
All the panels will load into separate layers.
You'll notice that they have black backgrounds so you need to get rid of it.
Select the Magic Wand Tool - Tolerance 0, Anti-Alias on, Contiguous on and delete all the black backgrounds in each layer.
Be extremely careful not to move any panel even the slightest. They're accurately registered remember?
At this stage you'll see your
mosaic although it is not blended at all.
Next select all the layers then Edit > Auto-Blend Layers > Panorama and tick 'Seamless Tones and Color' then press OK
After a little while you should have a complete blended
mosaic with no seams to start working from.
Have fun.
do you expect me to understand all of that stuff, at my age, 
I think I will just stick to the easy stuff I know. 
