Is 64 bit windows on it?? No point getting 8 GB if youre using 32 bit
According to the HP site
Dual channel memory architecture
Two DDR3 DIMMs (240-pin) sockets
PC3-8500 (DDR3-1066)
PC3-10600 (DDR3-1333)
Non-ECC memory only, unbuffered
Supports 1GB, 2GB, and 4GB DDR3 DIMMs
Supports up to 8 GB on 64-bit systems (DIMMs run at DDR3-1066)
Supports up to 4 GB on 32-bit PCs
*32-bit PCs cannot address a full 4.0 GB of memory.