it does say rw on the disk
Here are the specs on your burner:
Pressed SL DVD-ROM Read - 5X to 12X (CAV)
Pressed DL DVD-ROM, DVD+R/RW, DVD-R/RW Read - 3.3X to 8X(CAV)
Pressed Data CD, CD-R, CD-RW Read - 17.2X to 40X (CAV)
CD-DA - 4X (CLV)
DAE - 17.2X to 40X (CAV)
DVD+R Write - 6X to 8X (ZCLV) DVD+RW Write - 4X (CLV)
CD-R Write - 16X to 32X (ZCLV) MS CD-RW Write - 4X (CLV)
HS CD-RW Write - 10X (CLV)
US CD-RW Write - 16X (CLV)
As you can see, in some cases 4x is all the writing speed you are going to get. I guess we need more details on exactly what type of CDs you are using. As a rule, RWs burn very slowly. Rs are much faster (in your case up to 32x).
Also, BlackSpyder is correct. There is a way to adjust the burning speed with NERO. Look closely at every window you are shown as you set up the burn to find this selection. However, as I said, in some cases 4x may be all you are going to get, depending on what media you are using.