PxT gave a good reply. I'll add a few things, perhaps it will be helpful
By your post, I assume that you want to have users connect to your servers/services via the Internet to save the cost of having a bunch of dial of lines; the model is very much the same (not exactly but good enough for your purposes) regardless of dial-out to the Internet of dial-in from the Internet. Either way requires connectivity to the Internet.
Before jumping off to books on VPNs, Firewalls, and complex HOWTOS, it is essential that you design architecture based on your actual needs (requirements). You may not need VPNs or even a complex firewall, if your model is simple enough. On the other hand, if your model is complex, you may need a lot of gear/gadgets/configurations.
Keep in mind that that technical people, often fascinated with the technology, forget that the more complex you design a network (any system) the more it costs to sustain, maintain, and keep secure. Every line in a configuration file increases the cost of operations and ownership.
Network management experts estimate that the costs of manageing a network (and the power of the network) goes up with the square of the number of nodes on the network (N SQUARED LAW).
In a nutshell, more important than technology buzzwords is a clear roadmap on what your company plans to do and the risk management requirements and business processes. The number one mistake that I see people make is 'too much technology' and not enough planning. Keeping costs down and acquiring a high return on investment requires investing time in planning and design before considering the technical options and marketplace buzz.
[Edited by Neo on 11-09-2000 at 11:31 AM]