Question that needs to be answered soon please guys? Thanks very much

Hiya everyone,

My girlfriend really wants to be able to play H.D films and t.v programs on her computer and when she tries at the moment it is far to laggy to watch. Here are her current P.C specs, Dell Optiplex GX280, pentium 4 2.88GHZ, 250gig SATA hardrive, Nvidia 7200gs low profile, 220Watt psu, windows 7 ultimate. Its not amazing for some things but it certainly does the job. If i upgraded her GFX card to a HDCP card like am running Radeon 4650 low profile. ( A 512mb about 1.5GB virtual memory ) would she be able to run H.D ok?

Thankyou so much for any comments helping me.

Adam