I went to HP's tech support page (http://welcome.hp.com/country/us/en/support.html
), put in your computer's model (Pavilion a630n) and made sure I had the "See support and troubleshooting information" radio button hit.
From the page that it gave me, I clicked "Product Specifications". On that page (the link up top), you just scroll down.
Memory Installed - 512 MB
Maximum allowed - 4 GB (4 x 1GB) requires the replacement of the installed 256 MB DIMMs
Speed supported - PC3200 MB/sec
Type - 184 pin, DDR SDRAM
DIMM slots - Four