With just stock HSF I would not do over 400 on the core and no sinks no more than 730. You will know when its too high with the snow breaks out.
Mobile Barton 2500+ @ 2420mhz 11x220 1.7v
Asus A7N8X Dlx 440 FSB
1gb Geil GD pc3500 Dual Channel (2-3-3-6)
Segata 80gb SATA 8.5ms seek
ATI Radeon 9800 Pro(420/730)