12:50 a.m. on April 13, 2007 (EDT)
This has been discussed in this forum before. If you search down a bit, you can get some of the earlier discussion.
Basically, there is little difference among ski, hiking, trekking, snowshoeing and "Nordic walking" poles. There are some very specialized variations, like the radically bent versions used by downhill ski racers. But if you get the right length for your activity, it doesn't matter a lot what they are called.
The major differences are, as Tom noted, adjustable vs fixed length, with and without "shock absorbers", and the various size of baskets. The baskets are usually interchangeable within a given brand - none for just hiking, small for firm snow/mud/etc, larger for powder snow. Some are much lighter than others, some have different "swing weights" (basically where the weight is concentrated). The material makes a difference in weight and balance. Years ago, the best poles were bamboo, but you can only rarely find those now. Most poles these days are aluminum. Aluminum comes in different grades with the strongest for weight (hence the lightest) costing a lot more. An increasing number are carbon composite, space-age materials. The whole pole may be carbon fiber, or just the lower part of some adjustable poles.
Major point on adjustables is you can vary the length for conditions, including having different lengths for the up and down hill poles. For flat-ground travel on skis you want longer poles, while for skiing down a hill, you want shorter poles. Hiking uphill most people want shorter poles, and downhill longer poles (though some like it the other way around). Adjustable poles let you change as conditions change.
For my daily hikes, I use a pair of REI adjustables (no shock absorber), make by Komperdell, bought on sale for $20. They are just fine and I have used them for snowshoeing as well. My wife has a pair of REI (Komperdell) adjustables with shock absorbers. But after a couple hikes, she locked the shock absorbers out. For expedition use, I use a pair of Black Diamond Expedition FlikLok adjustables, with no shock absorbers. The FlikLok is a lot more dependable and lasts longer than the twist-lock type. But BD is much more expensive. The BD Expedition is 3 section and stores small enough to put in my checked luggage for the plane. I use these for hiking on trails for approach with heavy loads of climbing gear, hauling sleds up glaciers, skiing, snowshoeing, just all around use when travelling elsewhere.
For skiing (especially backcountry), I use a pair of Black Diamond carbon fiber probe poles. These double as avalanche probes, just in case, as well as being very light and having a good swing weight. They are FlikLok adjustable. I have tried Leki's carbon fiber adjustables as well and really liked them. I sometimes use the probe poles for hiking, such as during an approach to higher altitude slopes to get to the snow.
Basically the brand doesn't really matter a lot among the top brands. Komperdell, whether under their own name or with the REI label is less expensive and good for most purposes. Leki and Black Diamond are 2 of the top brands. I would probably suggest for your first pair, just go to REI and get a pair of their adjustables, with or without shock absorbers, when they are on sale (spring sales are coming up). These are cheap enough that if you want to change after a year or so, having gained experience and developed your own preferences, you can change to ones more suitable for your preferences without much loss.