If you are going to be in Beijing for at least a few days and will be using the subway system (and/or the buses) frequently, then buying a yikatong card can save you time and hassles from queueing for individual tickets. At the manned ticket window, say "yikatong." There is a RMB 20 deposit for the card (refundable when you return the card at the end of your stay), then you add on whatever fare amount you want. At RMB 2 per ride x "X" rides per day, you can figure RMB needed to charge up. Note that unlike the card deposit fee, unused stored fare on the card cannot be refunded so don't charge beyond what you'll need. If you need to add more value to the card, you can do so at attendant booths or at recharge machines (English menu instructions available). If you get stuck, someone can help you. It's a pretty user-friendly system even for the non Chinese speaker/reader. It's also one of the best financial deals going and a good way to beat Beijing's horrible traffic.
If you are only going to do a scattered ride here or there during your stay, just buy individual tickets as you need them.

VPN's work, but get the software loaded onto your computer before you arrive, and test it out. Get an SSL or OpenVPN GUI-based system, not a PPTP-type which may be cheaper but is now blockable. Make sure the VPN company knows you will be in China, as sometimes there are some extra 'tricks' you need to do (flushing the DNS cache and rebooting, etc.) to ensure performance from behind the Great Firewall.