My first recommendation is to make sure you are running the latest driver for the card. This is the Latest from the Dell site.
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Also check your security connections. Limited connectivity is commonly an issue with security setting/firewall settings
The 1545 is suppose to have a 1397 b/g mini wireless card. If you are upgrading to a N card, either the DW1510 or the DW1515 is a/b/g/n compatible, and the Dell Inspiron 1545. I know for a fact the DW1515 works flawlessly, and both are Dell recommended.