I had reasons to contact IAR regarding some other issue and inquired about your post and here was their response:
fprintf/fputch is not really supported in embedded environment , it is there part of the C runtime library, in embedded development you do not have File system, unless you are using an RTOS for example writing to a hardware SD card. If you want to use it you must customized the fputch to output the data to hardware device like an SD card. -IAR Support
IAR do not provide the File System specific code within eW430. This can be added by using FAT 16 libraries from the MSP430 Power Pack software from IAR or alternativly HCC Embedded (google it…) provide non FAT based software which will work with SD/MMC/NAND/Dataflash memories etc. HCC can provide FAT16 format or their own inplementation which is not FAT based but is a smaller footprint.
IAR have a demo version of power pack for MSP430 which will allow access to one file at any one time.
Both HCC and IAR products are expensive and not very accessable to experimenters.