Apologies for reviving an old thread but I've got some information here which I thought might be of use to the original poster of this thread.
I can confirm that it is possible to replace a CD-ROM drive in a Compaq Evo N610c Laptop with a DVD Rewriter drive as I have just done this myself.
The old drive has a casing holding it together. It's all held in place with smallish cross screws. So you might need to buy some regular instrument screwdrivers to prise the casing off. I'm lucky because I've already got a wide range of different screwdrivers lying around the house so it's not a problem for me.
There were 3 screws at the back holding in the ATA/IDE converter board and there were 2 screws holding in the two sides to the drive (4 screws).
Once the back panel ATA/IDE converter board comes off, you then have to take off the two side panels. The right hand side can be quite tricky to take off and I suggest you use a torch when attempting to get your screwdriver into the little screwholes.
All of the casing needs to be attached to the new drive. Like I said, the right hand side is very tricky to attach - you're going to need a very steady hand in order to get those tiny little screws into the screwholes. I'd suggest putting both screws into the holes square on before attempting to attach and screw in the right hand panel to the new drive.
The left panel is pretty straight forward and I don't think it needs explaining.
Anyway, this is the drive that I ended up getting:
My new DVD Rewriter drive is now working fine in my Laptop.
@rinrinrin, if you're in the UK, then you might wanna consider purchasing the same drive that I did.