Tire sizes and rim compatability

[Outrail]

Got a question on rims, tires and the like. If you can point me towards any obvious info sources that would be awesome.

I've got a 1999.5 pathfinder on 16 inch rims, and the M&S tires on front were pretty bald which isn't great for winters up here in Canuckistan. So I put on some decent, slightly larger second hand tires on the front but (like an idiot) forgot that while different tire sizes isn't the end of the world it is when you engage 4WD (and these weren't great for snow to begin with)

So I need winter tires. I'm also poor and can't afford new rims and tires so need second hand, and since I'm in the middle of nowhere finding 16 inch 6 bolt pattern tires and rims is a nightmare. So two questions really.

1) Wheelsize.com (http://www.wheel-size.com/size/nissan/pathfinder/1999/) indicates that as a 170hp my PF takes 16 inch tires (245/70R16 or 255/65R16). Can I drop down to 15 inch tires? Reading online I think I can but don't want to shoot myself in the foot. If that's possible finding tires just got so much easier.

2) Assuming yes to the above, will 265/70/R15 Geolanders on rims from a 2002 Nissan frontier fit on my PF? I'm thinking 'probably' but again, don't want to screw myself out of a a bunch of money and a three hour round trip.

I'm sure I'm asking something pretty obvious but can't seem to find concrete information.

edit: Okay, looks like I can get a hold of some 235/70/16 firestone winterforces in pretty good condition. The rims I'm running are 245/70/16's, so I assume they should be good. Is that right?