nvidia change to ati

i was basing my new system around a asus a8n-sli premium with a 7800gtx but now am seriously considering an ATI 1900xtx and am wondering if the rest of the system now needs to be changed.

Here's what i started with



PC Builder Quotation # 2222137
Category Image Item Description In Stock QTY Price Ext. Price
Case AeroCool AEROENGINE2 Silver ATX Case 4X5.25 1X3.5EXT 6X3.5INT USB 1394 Audio W/ Side Window No PSU
(AEROENGINE2-SSP) (sku: 17335) 2-5 days 1 $98.88 $98.88
Processor AMD Athlon 64 3700+ Processor S939 San Diego 2.2GHZ 1MB L2 Cache 90NM Retail Box
(ADA3700BNBOX) (sku: 14828) In Stock 1 $293.97 $293.97
Motherboard ASUS A8N-SLI Premium ATX S939 NFORCE4 SLI DDR 2PCI-E16 2PCI-E 3PCI SATA RAID Sound GBLAN Motherboard
(A8N-SLI PREMIUM) (sku: 15495) In Stock 1 $242.82 $242.82
Memory OCZ EL Platinum REV.2 (TCCD) PC3200 1GB 2X512MB DDR CL 2-2-2-5 184PIN DIMM Dual Channel Memory Kit
(OCZ4001024ELDCPER2-K) (sku: 12961) In Stock 2 $205.86 $411.71
Floppy 1.44MB Black 3.5IN FLOPPY DRIVE
(BLACK-FLOPPY) (sku: 6139) In Stock 1 $9.75 $9.75
Video Card BFG GeForce 7800GTX OC PCI-E 256MB 256BIT GDDR3 Dual DVI HDTV VIVO SLI Ready Video Card
(BFGR78256GTXOC) (sku: 15488) In Stock 1 $654.27 $654.27
Power Supply Antec True Control 2.0 550W ATX12V V2.0 Power Supply W/ Control Panel & 120MM Fan
(TRUE CONTROL II 550) (sku: 15900) 2-5 days 1 $118.56 $118.56
Sound Card Creative Sound Blaster X-FI Xtrememusic 24BIT Sound Card
(70SB046000008) (sku: 16551) In Stock 1 $139.03 $139.03
DVD-ROM LG 16X Black DVD-ROM 48X CD-ROM IDE UDMA33 INT OEM
(GDR-8164B-BLACK) (sku: 8984) In Stock 1 $27.26 $27.26
DVD Writer LG GSA-4167B 16X DVD+-RW 16X Dual Layer Writer IDE 2MB Black OEM W/ SW Burner
(GSA-4167B) (sku: 16202) In Stock 1 $56.24 $56.24
IDE Hard Drives Western Digital Caviar SE16 250GB SATA2 7200RPM 16MB 8.9MS Hard Drive 3 Year MFR Warranty
(WD2500KS) (sku: 16141) In Stock 1 $135.99 $135.99
Keyboard LOGITECH MEDIA KEYBOARD Black ULTRA FLAT DESIGN W/ AUDIO CONTROLS & ENHANCED FUNCTION KEYS
(967415-0403) (sku: 15169) In Stock 1 $29.67 $29.67
Mouse Logitech G5 Laser Gaming Mouse 2000DPI USB Bilingual
(931376-0215) (sku: 16284) In Stock 1 $74.31 $74.31
Speaker Logitech Z5500 Digital 5.1 Speakers 500W RMS SILVER-BLACK Analog Coax Optical
(970115-0403) (sku: 12847) In Stock 1 $346.28 $346.28
17" Monitor Viewsonic G90F 19IN 18VIS .25MM 16X12 Colmon TCO99
(G90F) (sku: 6067) In Stock 1 $272.52 $272.52
Operating System MICROSOFT WINDOWS XP PROFESSIONAL OEM (WITH SYSTEM ONLY)
(E85-03014OEM) (sku: 6527) Yes 1 $159.98 $159.98
Full assembly and testing of the system. $0.00
YOUR TOTAL
All quoted prices are in CANADIAN DOLLARS $3,071.24

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the ATI is only about a 100 more than the gtx and might be worth the expence
please tell me what the best possible changes that can be made to accomadate the ATI card
money is no obstical(except for the processor cause i already know this is a middle line processor and hope to upgrade later to a fx-57 or 60)