Are there any good firefox download accellerators?

if i download some big files, i need to go fast. what can i use to boost the speed to >400 kb/s?

system specs:
dell dimension 2400
intel p4 2.53 GHz
512mb RAM
win XP home
250gb HD

Answer:
good system my friend, congrats, impressive...
but no software, i mean no software can boost you that much.

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