What are you using now? Are you doing videos or just audio files?
I'm not particularly experienced with virtual DJ, however I would think any reasonably modern computer should have enough horsepower to do about whatever you want from an audio standpoint. You may well served to examine what all extraneous programs are running in the background before you go out and buy a new computer. That said, if you want to get serious I would highly recommend having a dedicated laptop for DJing.
Also, what are you using for a sound card? Are you using something that supports ASIO, and are you using that driver? ASIO made a huge difference in reliability for us. Basically gives the software a direct path to the output device--bypassing computer OS--as I understand it. We used to use Echo Indigo DJ sound cards--switched to Numark DJIO a couple years ago. The Echo stuff is nicer than the Numark--and VERY reliable when used with ASIO driver. If I just had one system I probably would have bought the newer echo sound cards, but didn't want to be locked into a specific card slot form factor (last I knew they didn't offer anything USB). That said, the DJIOs are fairly inexpensive and have been reliable... the Echo have much stronger output drivers, though.
