upper strut nut question...

[jnbjones@boulder.net (Jason Jones)]

Hey Guys,

I am about to undertake my first strut replacement and am worried about
being able to remove these nuts.  Is it impossible to do without an
impact wrench?  Also, I was thinking it would be safer/easier to get
leverage if I were to use the spring compressor with the strut still on
the car and then once the nut is loosened remove the strut and proceed. 
Any issues with this?  I don't have any kind of a vise to secure the
strut if I attempt it with the strut removed.  Also, would a shop be
inclined to swap the cartridges for me even if I didn't purchase them
from them and if so, what would be an appropriate charge?

Thanks,
Jason.