right so....
internal optical, boots from disc and preparing to install with blue and white progress bar for 3 hours plus!
external usb optical from 2007 imac, same as with internal drive.
external usb optical from a windows laptop, same as with internal drive
external firewire optical (acer brand), same as with external.
Conclusion, failing internal IDE HDD?
Tried with 10.4 and 10.5 install media.
Weekend will try target mode and my ibook to try install.
before tried all this it booted and worked fine from internal HDD.
This does not mean the HDD is without fault of course.
Will update after weekend.