Seriously Viking, 100Hz on an LCD is going to make bugger all difference... certainly not worth any extra money for it! (charging extra for this is robbery anyway for various reasons!) LCD display technology is nothing like CRT and doesn't suffer from the same issues. CRTs' phosphorous gets hit by the beam and glows briefly before fading again. This light-up time, and time-to-fade had to be critically timed so that you got a quick response, and long enough 'glow' but had faded enough in time for the next scan. Phosphor is passive of course, so inherently there needed to be a 'dark' period in between scans... it can't just instantly turn off ready for the next pass! This dramatically emphasised the flicker. The best way of reducing this was to make it fade twice as fast, but double the scan rate - thus minimising the 'dark' period.
LCDs are active - they have a light behind the LCD which shines through continously, and each pixel is 3 coloured transistors that are set to different levels of tranparency. So there is never any 'dark' period. Of course there are still issues of basic refresh - the more frames per second the smoother the motion, but all sources are basically 24/25/30/50/60fps, typically 25 or 30... so refreshing the screen 100 times per second isn't going to benifit you, really. For LCD the more critical issues are contrast ratio (try for at least 10,000:1), response time (try for 8ms at most, 5ms, better yet), and how even the black level is on a completely black screen with the lights down (the transistors are never completely identical - on cheaper LCDs this can result in patchiness when they are trying to block all the light from the backlight. Obviously, you also want the blackest level possible with this screen)
These parameters, or better will give you a well defined colour in your picture, viewable in all lighting conditions and with movies that have lots of dark scenes, and will also ensure that movement is clear an unblurred. The only other thing I would say is, beware that many manufacturers say their panels are HD when in fact they are nothing of the sort! Often only 1366x768 - you need to find the "Native Resolution" of the panel and this can sometimes be difficult... don't rely on the salesperson, ask for the manual! Just because a display can display a 1080i/p image doesn't mean that is its native resolution.
EDIT: forgot to answer your other question. Yes HDMI/DVI are definitely a big benifit for image quality. Definitely do not use svideo or composite connections. Component as a worst case. Avoid VGA, ideally use HDMI or DVI (the same thing as each other for video, so you can use convertor cables without loosing any quality - on that subject, don't be stiffed into buying expensive HDMI/DVI cables... salespeople will tell you it can effect the quality - it can NOT! It is just as digital as a Cat6 cable, ie it either works or it doesn't... if it doesn't you will see immediately that on screen! $10 max for a cable)
