Not a big achievement, but I want to report that I could use the RTLSDR dongle with SDR# on a laptop running WinXP with an Intel Centrino 1.6 GHz CPU. I have reduced the sampling to 1 Msps and the machine was running at 50% CPU: not bad for a 2004 computer! I listened to both WFM and SSB signals. There is probably room for a higher sampling rate, but keep in mind I have been listening to decoded output and not fed it over to another software (which in turn uses its share of CPU cycles).