I had one of those too! Great chip for it's time. AMD no longer produces processors using that style of socket (Socket 939 if memory serves). You're basically looking at a new system at this point. Socket FM2+ (for APU chips that have integrated graphics) or Socket AM3+ (for CPUs that don't contain integrated graphics) are what are used today. If you aren't playing demanding 3D games, APUs are probably the better value.
Look up the CPU support list on your motherboard's website and then hit eBay. If it supports the 6000+ or 6400+ Windsor, or especially if it supports the 955 or 965 you'd see a nice performance improvement.