If you're doing it yourself, there's a bodgy (read: dangerous) way to do it. A mate of mine lowered my car for me, and I stood back & watched
while he did the bodgy part. We made sure that the springs were seated properly, and did a few "tests" on his driveway (start/stop, rocking the car, etc) to make sure they were firmly in place.
This method only works if the springs you are fitting are pretty damn low (ie Superlows). If the replacement springs are taller than the shocks you are putting them onto, you will have great difficulty trying to compress them!!!
Also, this was performed on a '91 Falcon, so it might not apply to your XM. If the step descriptions "make sense" regarding when you look at your XM's front setup, then by all means, have a bash :D
1) Undo strut from arm (arm has disc brake on the end of it + studs for wheel to bolt onto) <-- I'm not good with terminology!
2) Undo strut from shock tower (under bonnet). DO NOT undo the centre nut!!!1!!11!!1111 Only undo the three nuts that surround it.
3) Apply force to arm and move strut around until it comes out. Strut & spring should come out as one unit. Spring will be compressed!
5) Place spring + strut in a wood vice & do up bloody tight. Make sure the nut holding the spring onto the strut is facing somewhere that isn't breakable (ie not facing a window, or a shelf full of expensive tools)
6) Cover spring/strut with a heavy blanket, except for end with nut.
7) *Gingerly* undo the nut with a long armed spanner. Continue until the nut comes loose and the spring uncompresses. This is the dangerous part. When my mate did his own EA, the spring shot off violently and nearly went through a door! When he did my EB's struts, the springs made a little "pop" noise and didn't go anywhere, due to the vice being wound up TIGHT and the blanket "muffling" the decompression.
8) Slowly undo vice, so that spring & strut don't drop out.
9) Replace old spring with lowered spring
10) Replace nut & "washer" or whatever it is that holds the spring in. Make sure the rubbers from both ends of the strut are seated properly into the spring.
11) Reverse steps 4, 3, 2, 1.
12) Repeat 1 to 11 for other spring!
Finally, ONLY do this if you're a risk taker. Personally I wouldn't have done it myself, but since my mate thrives off doing things the wrong way, I was more than happy to watch him risk injury