Your internet connection is finite. Adding adapters will not change the download speed.
More information is needed about the specific sites, your system, type of broadband connection. Your question is light on information.
I have a network adaptor already but after the initial burst of speed at as fast as 240kB/sec it slows to 10kb/sec or less. Can I install a secong network card and use a fast Ethernet switch to get a combines speed that improves this performance?
If not, where to look to reduce or eliminate this slow down in the connection rate?

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