First off, take a look at this:
Graphics Card Hierarchy Chart : Best Graphics Cards For The Money: April 2012
It's a good quick reference on what kinds of graphics cards (cores) are equivalent / better in comparison for the last 10 years or so.
The two cards you listed are pretty low on the graphics power side of things, but they'll work perfectly fine for business applications. They're both quadruple core setups on a single card, so you'd get the full power of each graphics processor for each monitor. That's good if you're going to be doing hardware accelerated video playback via separate streams on each monitor. Blu-ray and streaming 1080p h264 video is about all those graphics cores will be good for though.
If you want to do any gaming, you're going to have to start wandering up the chart in power. The HD3450 is 6 up from the bottom, and the GF210 is 4 up from the bottom... they're about equivalent to the GeForce 6600 that I bought 8 years ago when it wasn't quite top of the line- right when everything started to migrate from AGP to PCI-E. That's how old.
The card I have right now is an MSI GeForce GTX 560 Ti Hawk (384 core) that's ridiculously overclocked from the factory, about equivalent to a standard GTX 570 or slightly faster- which is 4 lines from the top of that list. It's already considered one or two generations old- it was the hot card at the very very beginning of 2011. Regardless, it's still a pretty good graphics card for gaming, and can run practically anything on the market right now at best or pretty damn close to best settings at 1920x1200 resolution with nice smooth 60fps+ frame rates. You can get them new for right at about $200 (just looked it up, weird because I paid the exact same a year ago).
All this said, almost all of your graphics cards these days- especially the ones that provide just slightly more than the minimum business required level of performance- support dual output from a single card. My 560Ti runs dual monitors with no problem, and so will something as lowly as a GeForce GT220. If you just want three monitors for office work, grab two cheapo cards with dual outputs (DVI + VGA + HDMI is most common, with 2 functioning at a time) and plug them both in. You'd be done for about $50-60 total, and not have some weird 4 core configuration that might have proprietary drivers and all sorts of other problems. A cheap $20-30 GF210 would do fine. I see cards for free after rebate (and only $30 out of pocket to start with) all the time at Fry's.
If you want to game and are ok with just using one monitor while blowing someone's head off, pick up the best $200-300 gaming card you can justify dropping a load of cash on, then grab one cheapo card and run your side monitors with it. That's what I do- you get economical desktop real estate with gaming/CAD power on your center monitor. I'm running a widescreen 24" 1920x1200 IPS screen in the center with my old 20" IPS 1600x1200 screen on the side- and I'm looking for an identical 20" to go on the other side. The main screen is powered by the 560Ti, and the sub screen(s) by an older GeForce 8600GT.
So what exactly do you want to tri-monitor setup for?
