
HP Product Site
Maximum memory
4 GB
Memory slots
4 DIMM slots
Memory upgrade
Expandable to 4 GB DDR2 Synch Dram PC3200/PC4200 (400 MHz, 533 MHz) Non ECC
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Siversmith[PCD
Get new motherboard and ram!

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Siversmith[PCD
That 3.5 will also only be valid if you have told Windows about them. There is actually a 3G switch that you need to apply in order for your windows to know that it has more ram. Here is a good article on this matter.
http://blogs.technet.com/askperf/archive/2007/03/23/memory-management-demystifying-3gb.aspx