If you use the right VST plug-ins, it easy to saturate ANY cpu, no matter
how powerful it is. ;-) They all have different amounts of CPU load... there
are light-weights and heavy-weights. For example, a convolution reverb
plug-in will easily require a big CPU load, whilst you might instead load 20
eq plug-ins to put stress on your CPU...
Of course, you can get a DSP card, like the UAD-1, TC PowerCore, SSL
Duende - BUT neither of these will work with standard VSTs, they only accept
specific proprietary plug-ins! I haven heard of a card, that can be used
for standard VST plug-ins yet.
About anything is "more professional" than the SB live you mentioned below.
Rather get a card with a real and well-written ASIO drivers. Many people get
along well with the "M-Audio Delta Audiophile 2496". Good drivers, better
sounding converters and even cheaper than a current Creative Audigy card.
Should be around 100 US$ or less. Big improvement over a SB live!!!
RAM has become dirt cheap, get as much as possible in your machine
rather a work-around, than a serious sound card