moving files to external HD

Hi. This is more of a HD question rather then a software question so I guess this is the right forum.

I'm new to mac and I've run into a problem moving RAW and JPEG files around. I'll start off with the equipment being used.

A new IMAC 1TB HD.
Model Name: iMac
Model Identifier: iMac8,1
Processor Name: Intel Core 2 Duo
Processor Speed: 3.06 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 6 MB
Memory: 4 GB
Bus Speed: 1.07 GHz
Boot ROM Version: IM81.00C1.B00
SMC Version: 1.30f1

A simpletech external HD with 150 GBs. The existing files mostly photo's were written with windows XP.

A HP photo printer with a built in card reader.

The problem is if I want to send photo's from my card reader, mac HD to the external HD it wont let me. It tells me that-

Picture could not be saved because write access was not granted.

I can move photo's from external HD to my mac no problem, it just wont work the other way.

Does anyone know of a fix?

The Simple Tech external hard drive is formatted to NTFS. (I have one also.) Mac OS X can read but not write to a drive formatted to NTFS without the use of a third party driver. I recommend Paragon NTFS rather than the free NTFS 3G MacFuse combo.

Paragon NTFS can be purchased from here.

If you would like to try the free NTFS 3G MacFuse go here.

Regards.