I have had this situation more than once over a longer period of time.
I have not tried roll20, though I have tried other computerized tools.
For easy online collaboration (adventure log, maps, calendar, etc.) the award-winning Obsidian Portal works great.
My group uses Ventrilo as a push-to-talk voice tool for the Internet.
Then I spend a bunch of time before sessions setting up gridded maps, the characters, creatures, etc. in the d20pro tool which allows for a graphic, 2D counters/tokens-based virtual table-top play. Attacks and spells can be configured to buff, attack individual or templated groups, etc. So there is a certain amount of automatic calculations allowed. This is different from VTT's where the intention is to facilitate talk and dice rolls and perhaps move figures around on the map, but there is no automatic calculation of (modified) attacks, saves and skills versus AC and DC's. Each group has its preferences for such things.
That is my online D&D gaming stack for 3.5. My friends and I now play remotely, including those in the same town, because of the convenience.
There are plenty of other tools/configurations that provide for sharing resources and having a virtual tabletop with voice and chat for play. Fantasy Grounds and Battlegrounds are other proprietary VTT's. The Battlegrounds RPG site has an extensive Links section with a good selection of free and $ tools (including his competitors).