I'm planning to upgrade my system memory for more performance.
Currently, I have 767 MB RAM. (128-256-128-256)
My motherboard only supports DDR.

I was thinking about replacing the two 128s with two 1 GBs. Will be a total of 2,5 GB DDR RAM.
But is this possible?

My computer info:

Computer
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- Manufacturer: NEC Computers International
- Computer Model: POWERMATE ML6
- Computer Name: MARTIJN
- System Type: x86 (32-bit) system

Motherboard
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- Manufacturer: NEC COMPUTERS INTERNATIONAL
- Model: PALOMAR (MS-6763)
- BIOS Manufacturer: Phoenix Technologies, LTD
- BIOS Model: AwardBIOS v6.00PG

Processor
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- Model: Intel(R) Pentium(R) 4 CPU 2.80GHz
- Clock Speed: 2800 MHz

Memory
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- Size: 767 MB RAM

Harddisk
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- File Format(s): NTFS, NTFS
- Size: 191,66 GB (38,28 GB + 153,38 GB)
- Free Space: 98,33 GB (22,18 GB + 76,15 GB)

CD-/DVD-ROM Drive
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- Model(s): PIONEER DVD-RW DVR-112D, YU0540X LER809K SCSI CdRom Device
- Type(s): CD- or DVD-ROM, CD- or DVD-ROM

Sound Card
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- Manufacturer: Analog Devices, Inc.
- Model: SoundMAX Integrated Digital Audio

Graphics Card
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- Model: Radeon X1650 Series Secondary
- Video Processor: ATI Radeon Graphics Processor AGP (0x71E7)
- Memory Size: 512 MB VRAM
- Driver: ati2dvag.dll, versie 6.14.10.6891

Display
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- Manufacturer: (Standaardbeeldschermtypen)
- Model: Standaardbeeldscherm
- Screen Resolution: 1024x768
- Color Depth: 32-bit
- Refresh Rate: 85 Hz

Mouse
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- Manufacturer: (Standaard-systeemapparaten)
- Model: USB-HID
- # of Buttons: 5
- Connection: USB

Keyboard
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- Model: Standaardtoetsenbord (101/102 toetsen) of Microsoft Natural PS/2-toetsenbord
- Type: Uitgebreid (101 of 102 toetsen)
- # of Function Keys: 12

DirectX
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- Version: 9.0c

Operating System
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- Name: Microsoft Windows XP Professional
- Version: 5.1.2600
- Service Pack: Service Pack 3

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What is the max amount of memory total and per slot?

When scanning using http://www.crucial.com/, I see max total is 1 GB and max per slot is 512 MB. Is this true?
Also mentioned is that I don't have dual channel and 2 slots on my motherboard, which is wrong, so I don't know.