Everyone can play RMVB (Real Media Variable Bit rate) format without any problem with  Real Player, But if you want to play this file in PSP ( Play Station Portable) you can’t directly play because PSP ( Play Station Portable) support only mp4 file format , so first change your file format so that you can play your file without any problem.
For changing your file format in mp4,  XviD4PSP 5.0  may be good choice for you and you can convert your file easily with this software

XviD4PSP 5.0  support many file format like
Import formats:
AVI DIVX ASF MPG MPE M2V MPEG VOB TS M2P D2V MOV QT 3GP HDMOV RM RAM RMVB RPX SMI SMIL MKV OGM WMV DVR-MS PMP FLV.

Export formats:
PMP AVC, MP4 PSP AVC, MP4 PSP ASP, MP4 iPod, MP4 iPod 640, MP4 iPod Touch, MP4 iPhone, MP4 PS3, MP4 Xbox 360, MP4, AVI, AVI DV PAL, AVI DV NTSC, AVI Hardware, MPEG-2 PAL, MPEG-2 NTSC, MPEG2-TS, MPEG2-PS, FLV, MKV.

Download free XviD4PSP 5.0 here