You sure can Davo.
You'll need to remove the drive from the enclosure,,which is very simple and straightforward.
There is a Jumper on the Drive,,,it should be set to CS/Cable Select.
The Drive should have a label which depicts the jumper settings.
If Not,,Samsung's website has simple instructions I'm sure.
You'll also need a ATA Cable,,,ATA 100/133.
There's OLD ata 33 cables ,but I doubt you'd happen upon one of those these days.
That cable is $5 USD or so,,,,
You'll also need 4 little screws to mount the drive,,and that's
all the additional parts you'll need.
The cables have a "Motherboard end" and a drive end.
Most All have dual Drive Connectors.
To Identify Motherboard end,,Cable will be either:
*Labelled
*Blue or Colored Connector
* Or have One connector a far distance from the 2 Drive Connectors
(board)-------(HDD)-(HDD)
Looking Into your PC,,,the ATA/EIDE Connectors are on Far Right Hand side.
Use the #1Connector,,it's the extreme R/H one
They're pictured here directly above "BIOS" chip
If Your CD/DVD Drive happens to be plugged into #1 IDE Connector,,that's fine.
Just use # 2 Connector,,,,there's No Problem whatsoever with that.
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00378480&lc=en&cc=us&dest_page=prodinfoCategory&tool=prodinfoCategory&query=Compaq%20Presario%20SR1520AN&dlc=en&product=1102915#
Lastly,,You'll need to Mount the Drive
Now that I've typed this all,,,
I see that Compaq has "HP and Compaq Desktop PCs - Installing or Replacing a Hard Drive"
with Videos and everything,,,lol
http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph03429&lc=en&cc=us&dlc=en&tool=prodinfoCategory&query=Compaq%20Presario%20SR1520AN&product=1102915&dest_page=prodinfoCategory#N817
If You Do have space in the "Drive Cage" to mount it,,,and have a choice of positions,,,it's best to mount the Drives Away from each other---like Skip a Space.
It's NOT necessary,,,only a suggestion in the interest of optimizing Airflow around all the drives.
You couldn't have chosen a Better Drive.
All Samsungs are excellent quality,,all their products are actually.
Your particular Drive is Fast,Quiet,Cool Running,,and arguably THE most reliable.
It's one of the most Overlooked & Underrated drives on the market.
Very nice addition to your PC
Hope that helps,,,Good Luck