When I ran a comparison between Bootcamp and Parallels (last October), I found Parallels lacking in a couple places and excelling in others.
The following is based on a 1.5GHz Core Solo Mini with 512 RAM:
Processor - 777MHz (P) 1.5GHz (BC)
Memory available to Windows - 178MB (P) 512MB (BC)
Network - wired OR wireless (P) wired AND wireless (BC)
Video - SVGA (P) 3D Graphics (BC)
Parallels also had some advantages over Bootcamp too:
Startup - from within Mac OS (P) Reboot (BC)
Sharing Data - Shared folders configurable (P) Mac can read windows, Windows not see Mac (BC)
Clipboard Cut N Paste - Installable as tool (P) None (BC)
OS Capabilities - Windows 3.11 to 2003, Vista, FreeBSD, OS/2, Solaris (P) Win XP Pro SP2 and above (BC)
(P) = Parallels (BC) = Bootcamp
It is possible Parallels is better now, but for lower end machines, the overhead of runnning Mac OS and Parallels and Windows doesn't leave much for the application you actually want to use. If you have the processor and memory for it and can accept the video and network limitations and feel the $79 is worth it, Parallels could do the job for you. Otherwise, save the money and just use Bootcamp. Either way, you need a Windows license.