I wouldn't invest much into getting this server working. The DL585 G1 is a bit old and was end-of-life in 2006. It's not supported under ESXi 5 and I'm not sure you'd be able to use 64-bit virtual machines within it. The VMWare hardware compatibility list implies that support for that model was limited to ESX 3.5.
Either way, the model you have was designed to work with external storage due to its limited internal drive space (4 hard drive bays). At the time, the preferred solution was an external SCSI MSA30 unit mated to a Smart Array 6400-series controller and later, the MSA20 and MSA60 units.
Please reference the detailed specifications and maintenance guide for the DL585 server.
You did not specify how much space you needed. Officially, the model can accommodate 4 x 300GB U320 SCSI disks (HP part #350964-B22). That's your path of least-resistance to maximize space inside the server. You can find the disks for $150US/each used.
The other option is to replace the SCSI drive cage with the SAS/SATA drive cage option (HP part #379090-B21). This will provide 8 x 2.5" internal SAS/SATA drive bays. You'd use this with a Smart Array P600 RAID controller. At this point, you could get away with nearly any basic 2.5" SATA or SAS disk (in an HP drive carrier), or look at the specific part numbers listed in the P600 quickspecs. SATA speeds will be limited to 1.5Gb throughput.
From this to this...
Any other solution will require an external storage chassis and an accompanying controller. Even used, those parts may not be worth the effort. It's old gear. BTW - The P600 controller is a bit of a dog. It was really a transitional product to help the migration from parallel SCSI to SAS.