I havn't been skiing in Chile, but I have visited Chile and know a thing or two about the resorts. Im also planning on spending a week in September there, and will be skiing for a day then conditions permitting!
First off, there are 4 major resorts in the Santiago Metro Area. 3 are located all next to each other and all of these three are within 50km of Santiago: Valle Nevado, El Colorado y Farellones and La Parva. The fourth major resort is Portillo, which is 2 hours outside of Santiago on the International Road that goes to Mendoza, Argentina.
Valle Nevado is popular for good reason, it has over 37 km of ski runs, 34 runs total. It has Chiles only high speed quad lift, a half pipe and ranges in Altitude from 2860 meters to 3670 meters. Views from the top lift at 11,700 feet include parts of Santiago, the Pacific Ocean, and the dominating Cerro El Plomo- 17,800 feet! It also ha a snowboard park and a halfpipe.
El Colorado/Farellones is the lowest altitude resort, spanning from 2430 to 3333 meters. Its a small resort with only 22 runs, only 3 are advanced and 4 are expert runs. Views from Cerro Colorado(10,900 feet) off the top lift however are more open, and include Cerro El Plomo and the Pacific. It has a snowboard park.
La Parva is higher up the road from El Colorado, and higher in altitude- from 2662 meters to 3630 meters. Its highest lift goes to 11,900 feet, and a towering cliff above called Cerro La Falsa Parva dominates at 12,900 feet. As the most westerly situated resort in the cluster, views are wide open to the many 15,000+ feet peaks surrounding Santiago, the entire Santiago Metro Area can be seen, as well as the Pacific and Cerro El Plomo. According to my Chilean Guide from Turistel it is "The Winter Center for most of the population". And for good reason, over 40 km of runs and over 3000 vertical feet make it the largest resort.
The fourth is Portillo- Arguably the most dramatic of the 4. Portillo is a small resort with only 5-6 lifts and most of the 30+ runs are blacks and blues. Portillo is sutated in a 1000 meter steep glacial canyon on the shores of Laguna Del Inca at 2880 meters. Views are a bit limited to the high peaks and canyons in the Andes with no view to the oecan- in no way like the slope views of the other three resorts. Highest lift goes to 3330 meters. Google image search "portillo" and you will soon see why this is a popular destination!
Have fun and good luck!!! If you would like more info I can pass along bus information to get to the resorts, the roads are narrow and winding and public bus transportation is not only reccomended, its also the way the vast majority of Chileans travel and quite comfortable!
Right now its July 2006- and Chile has had large snowfall totals this year! Great for skiing, but terrible for the flooding in the lowlands- over 25,000 chileans are homeless in the Bio-Bio region near Concepcion...