Using the flashget extension for firefox works very well, but flashget itself isn't a download accelerator, you still need to download one b/c all flashget does is integrate it into your browser. I advise freedownloadmanager, which, although it comes with a couple of reminders to donate, doesn't have any spyware/adware/malware, and can help speed up downloads significantly. You might want to rethink this if you don't have a lot of memory, b/c almost any dl accell. is going to use quite a bit. Thankfully, the latest releases of fdm have reduced the usage, so it shouldn't be too bad.
Also, you if you're using windows 2000/xp (no one should be using 98 or lower -_-; ... really...) you might want to check out
http://www.speedguide.net/files/TCPOptimizer.exe. It's a one time use and forget program that optimizes your internet/network settings and the associated registry files (also has no malware etc). You'll probably just want to select the "optimal settings" button and hit apply.
One final thing (I know this is kinda going away from dl accelerators, but it's still useful for connections/speed), is that windows xp has a limit (10) on the maximum number of half open tcp connections (don't worry if you have no clue what this means), and that can be a pain in the a** when using something like bittorrent, b/c it can severely slow down the rate of finding new peers to connect to. If you want to get around this limit, check out this link:
http://www.lvllord.de/download.php?url=en/...atch223d-en.zip which is a patch to edit the tcp.sys file.
----> Just as a little warning: Using the xp patch has sped up my connections and has not created any issues for me, but it is editing a main windows driver file (it also makes a backup automatically, just in case you want to revert back or something goes wrong), so there is slight possiblity that it will conflict with some other program on your computer (this has never happened for me). Lastly, some antivirus programs (bitdefender is the only one i actually know of) identify the patch as a virus. It's not a virus, so as long as you get it from the creator's page, which is what I linked to, you shouldn't have any worries, antivirus detect it b/c it modifies a system file, which is the whole point of the patch, don't worry ;D.
Good Luck downloading

-DEbob