DOSbox being an emulator and being Vista 64 bits compatible it shouldn't be more painful than running it on a 32 bits system. The only thing is to find the good DOSBox parameters so the game runs fine. Getting D-Fend is indeed useful if you don't want to mess with config files. It allows to configure via an UI what kind of computer you want DOSBox to emulate. You should keep the defaults set by D-Fend then adjust from there if needed. In general the only things you may have to adjust are the type and amount of RAM (32 or 64 MB generally work well) and the sound card (type, Address, IRQ, DMA -- Generally a SB16 with a 220 address, an IRQ of 5 or 7 and a DMA of 5 should work if the game truly supports standard hardware. However if that doesn't work with a SB16 you may try to switch to a SBPro, keeping the same parameters).
Note that you must run the game installer via DOSbox as well so the installer is able to see the virtual computer, including the sound card you configured. Most DOS games will refuse to install if a proper sound card doesn't exists.
DOSbox includes many other refinements but most of them are addressing the "look" of the game so for now just focus on the RAM and sound card as these are the most important to get the game running. Oh and yeah, you should push the "CPU cycles" parameter of DOSbox to a rather high value if the game appears to be sluggish. a value of 15,000 should be a good starting point for the most demanding games (D-Fend always tends to set this value too low with really old DOS games in mind). As Dark Forces is a 1995 game you should push the value comfortably high.
Running a DOS game in DOSbox can be pretty easy but the first time (as always with first times) you'll have to experiment a bit according to your own system.
