Im a currently working with 720x576 d1/dv pal footage in avid, and have exported from here to after effects as a same as source quicktime.
What composition settings should I use for this type of footage so that I don't lose any picture quality and am able to export as widescreen 16:9.
Interpret the footage normally -- don't change anything about it.
Then drag the footage into a PAL widescreen preset comp.
Next, you have two choices if the original footage was 4:3:
a) leave black bars on the sides of the footage
b) scale it up to fill the screen -- this will cut off the top and bottom of the footage and you'll lose a bit of resolution due to the enlargement..
These are your only choices if you want the footage to look normal and not strangely stretched. Pixel aspect ratios (PAR) are only to be used when making sure footage looks normal, that is, you interpret the footage with its native PAR and drag it into a comp using its native PAR. PAR is not used to make 4:3 fit 16:9 or vice versa.