Is this an integrated chip? If so, most will only support dual monitors on vga+dvi or vga+hdmi.
If it is a dedicated card, the radeon 5450, it will only support dual. (2 of any kind).
If you want triple monitors, get another card with it and just have 2 dedicated cards (not crossfire, mind you). I have 1x 5830 with triple monitors in eyefinity and a 1x 4850 with one DVI monitor and 1 Component HDTV, and it works flawlessly.
Gaming across multiple screens is called eyefinity. You must buy an eyefinity-ready card like 57**+. THIS is the solution you might want: Just buy one 5700's card instead and then buy an active Accell display port-vga cable for eyefinity. Voila! You got one dvi, one hdmi, and one vga via the adapter. Cost? Depends on you resolution. For my 5830, it was 200 for the card and 35 for the adapter. My three monitors are the exact same model, so it is 1:1 perfect pitch and contrast. Remember, eyefinity will chose the lowest resolution size of your three monitors and downscale the others to match it.
Keep in mind that your 3 monitors will probably have radically different PPI's, so if you do an expand setup with 2 cards, dragging windows or objects across the bezels will *work*, but they will most likely not match up, resulting in discontinuity.