Co-Locate Low Volume Web Server upgrade/migrate advise

Dear all I am currently hosting about 15 odd sites on my 1U
server running Dual AMD Opteron 248 w/6GB RAM. Due to lack of space
on the casing with only 1 x 3.5" bay, I put in 2 x 2.5" 500GB
5400rpm HDDs on an Adaptec SATA RAID 2420SA and it has been
running