We took the Royal Princess from Buenos Aires to Valpraiso Feb/03. www.portcompass.com
has a good selection of tours. We used them in BA and some of the other ports. We stayed at the Hotel Castelar in BA - it was okay. In Santiago, we stayed at the Hotel Orly - it was great. Check website. In a good neighborhood. Its more like a large inn - converted private mansion. It has about 30 rooms. Won awards for its preservation of a classic building. Nice people. By the way, Santiago is considered one of the safest cities in the world. Has a good subway too. email me if you need more info.
PS we are going back to see Argentina in November (not cruising). Fell in love with the place.