If you're
seriously looking to get an XC70, then you REALLY want to find a bit more money / opt for higher miles and buy the newest you can, certainly '03 onwards.
Pre '03 and they had a viscous coupling, post '03 and it's a Haldex unit.
If it's a car with a VC you must make sure all four tyres have the same diameter, to within 5mm (AFAIK) or you will get very expensive transmission damage. The Haldex cars do not suffer from this problem to any degree and can have tyres of different sizes, within reason of course.
There's plenty of threads, do a bit of reasearch and go into buying one with your eyes wide open, 'cos if you get a dud it'll cost ya big time....
The 163bhp D5 XC70 (>'05) will put a big smile on your face, particularly a manual version and do 40mpg+ in reality.
The '55 plate 185bhp cars will make you grin, embarrass the baseball cap brigade, and still do mid 30's. You can have it remapped to 240bhp+ I believe
BTW, are you aware of the later Volvo potential auto box issues as well? Applies to XC70 as well as S60/V70 models.