PowerMac G4 as video controller - upgrade how?

My parents are considering hooking up their old G4 PowerMac to their new 46" 1280p 120Hz Sharp LCD- Mainly so they can stream their favorite television shows when they miss their air time. It would be useful for use with Front Row since they've a large library of their movies ripped to the server and linked in iTunes.

The problem with both these media types is that the PowerMac just can't keep up. At times, it's as slow as a frame every 3 seconds. I'd like to give them a Christmas gift of making the machine work for them, but I'm not sure simple upgrades will do the trick.

I'd start with maxing out the RAM and getting a better video card. As to which kind would be most cost effective, I'm not sure. Below I list the current specs of the machine. As I've seen others ask upgrade questions and get answers, what does this PowerMac need to play non-high-def. videos? High-def video? All suggestions would be appreciated.

Specs:

Hardware:
Hardware Overview:
Model Name: Power Mac G4
Model Identifier: PowerMac3,5
Processor Name: PowerPC G4 (2.1)
Processor Speed: 867 MHz
Number Of CPUs: 1
L2 Cache (per CPU): 256 KB
L3 Cache (per CPU): 2 MB
Memory: 896 MB
Bus Speed: 133 MHz
Boot ROM Version: 4.2.5f1

ATA:
ATA Bus:
IBM-IC35L040AVER07-0:
Capacity: 38.35 GB
Model: IBM-IC35L040AVER07-0
Revision: ER4OA44A
Serial Number: SXPTXJL9663
Removable Media: No
Detachable Drive: No
BSD Name: disk0
Protocol: ATA
Unit Number: 0
Socket Type: Internal
Low Power Polling: No
Mac OS 9 Drivers: No
Partition Map Type: APM (Apple Partition Map)
S.M.A.R.T. status: Verified
Volumes:
Macintosh HD:
Capacity: 38.22 GB
Available: 11.62 GB
Writable: Yes
File System: Journaled HFS+
BSD Name: disk0s3
Mount Point: /
ATA Bus:
TOSHIBA DVD-ROM SD-R1102:
Model: TOSHIBA DVD-ROM SD-R1102
Revision: 1A18
Serial Number: 8171319486
Detachable Drive: No
Protocol: ATAPI
Unit Number: 0
Socket Type: Internal
Low Power Polling: No
Audio (Built In):
Built In Sound Card:
CODEC: Texas Instruments TAS3001C
Sample Rate: 44.1 KHz
Number of Inputs: 0
Number of Outputs: 3
Devices:
Output:
Type: Internal Speaker
Output:
Type: External Speaker
Output:
Type: Headphones

Disc Burning:
TOSHIBA DVD-ROM SD-R1102:
Firmware Revision: 1A18
Interconnect: ATAPI
Burn Support: Yes (Apple Shipping Drive)
Cache: 2048 KB
Reads DVD: Yes
CD-Write: -R, -RW
Write Strategies: CD-TAO, CD-SAO, CD-Raw
Media: Insert media and refresh to show available burn speeds
FireWire:
FireWire Bus:
Maximum Speed: Up to 400 Mb/sec
Graphics/Displays:
NVIDIA GeForce2 MX:
Chipset Model: GeForce2 MX
Type: Display
Bus: AGP
Slot: SLOT-1
VRAM (Total): 32 MB
Vendor: NVIDIA (0x10de)
Device ID: 0x0110
Revision ID: 0x00b2
ROM Revision: 1055
Displays:
Apple Studio Display:
Display Type: LCD
Resolution: 1280 x 1024
Depth: 32-bit Color
Core Image: Software
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Memory:
DIMM0/J21:
Size: 512 MB
Type: SDRAM
Speed: PC133-333
Status: OK
Manufacturer: Unknown
Part Number: Unknown
Serial Number: Unknown
DIMM1/J22:
Size: 128 MB
Type: SDRAM
Speed: PC133-333
Status: OK
Manufacturer: Unknown
Part Number: Unknown
Serial Number: Unknown
DIMM2/J23:
Size: 256 MB
Type: SDRAM
Speed: PC133-333
Status: OK
Manufacturer: Unknown
Part Number: Unknown
Serial Number: Unknown
Power:
System Power Settings:
AC Power:
System Sleep Timer (Minutes): 0
Disk Sleep Timer (Minutes): 10
Display Sleep Timer (Minutes): 20
Sleep On Power Button: Yes
Automatic Restart On Power Loss: No
Wake On AC Change: No
Wake On Clamshell Open: Yes
Wake On LAN: Yes
Wake On Modem Ring: Yes
Hardware Configuration:
UPS Installed: No

Thanks in advance for the help.