In reply to charliehl:
From what I've seen the a lot of the market for ski kit is aimed more towards fashion than technical function so it's possible that your mountaineering kit will keep you warmer and drier anyway. I've never bothered with a snow skirt and I've not missed having one, as David said make sure you overlap your layers and give yourself a good shake out if you happen to take a big tumble into deep stuff (unlikely as a learner).
I would recommend getting a couple of pairs of ski socks instead of walking socks as they do make your boots much more comfortable, I find them much better for cold winter days walking and climbing as well.
You could wear your waterproof trousers and be ok but I probably wouldn't. I worked a ski season and spent 90% of my days in softshell trousers (£15 from trespass), more comfortable and you're not risking ripping your waterproofs. Do make sure that they fit over ski boots if you go down this line though. It's worth looking on eBay as well as sallopettes are the sort of thing people will often wear for a week and discover that skiing isn't for them, I've seen them go for as little as £15-20 sometimes.
Hope you have great week!
Post edited at 21:42