Hmm, I will refine the list given above by Aniruddh
2X256 MB DDR400 RAM, for dual channel, Intel loves it.
Celeron D is also good but if she is goint to encode movies, Pentium 4 is better, ask her that, if she is not going for movies encoding or DVD ripping, then Get a Celeron D 2.8 GHz.
915GAV is good enough for her, although if found cheap go for Asus P5GL-MX
Syncmaster 793MB Monitor,
Logitech Internet pro desktop, Wireless
Lite-On combo drive SOHC-5236K, what's the use of this movie system without a DVD drive
Creative inspire T3000 speakers, or if affordable then go for iTrigue 3200
Samsung 120 GB SATA HD, with 8 MB buffer, 7200 rpm
APC 500VA UPS, will enough for this system
Frontech cabinet as they give a lot of fan installation options, install a rear exhaust & one side exhaust fan.
Colorsit M300U Power supply or equivelent, don't go for low quality brands for PSU