How can you speed up Windows XP program performance while another program is performing I/O operations?

On each of 3 PCs I use, Windows XP frequently slows to a crawl during various I/O operations (Disk access, network file transfers, network printing). Program windows are slow to respond to menu pull-downs, the mouse stops moving for a time, alt-tab switching slows, etc.

This is unacceptable. These are not slow PCs and CPU utilization is frequently not 100%. The user interface should always take top priority and provide positive feedback.

Is there a way to tell the system to use a larger I/O cache? Reduce the priority of certain I/O tasks? Keep frequently used operating system components in memory? Any I/O cards that specialize in offloading I/O duties from the CPU?

PCs I use: AMD XP1700 512Mb, P4-3Ghz w/1Gb RAM, Cel 2.9Ghz w/1Gb RAM. All running Windows XP Pro with all the updates and service packs. 2 Nvidia video cards, 1 HP integrated graphics. Hard drives vary, but I think each has at least 2Mb cache.

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[tags] 1gb ram, file transfers, networking printing program, nvidia [/tags]