Assuming that your Windows 7 laptop is working on the wireless network or wired for that matter you need to determine the actual IP address that the printer is using on the network.
There is a couple ways of doing this
First you can look into the router DHCP Client table and it should be listed there.
Or you can look at one of the computers that you actually have that the wireless printer is working on,
Open your printers folder and select then right click the printer (either the vista or xp machine) and choose (printer) properties. From the resultant dialog box select the "Ports" tab in the column header titled "Port" use your mouse to resize the column so you can view the entire port name by dragging the seperator bar to the right. Now assuming that it is not some super proprietary port it should include the IP address of the wireless printer, something in the 192.168.0.nnn range. Write that down.
Now on the Windows 7 laptop open devices and printers and select add printer from the menu bar then select "Add a local printer". Then select the radio button that says "Create a new Port:" and use the drop down box to select "Standard TCP/IP Port" and click next. In the "Hostname or IP address:" text box enter (type) the IP address of the wireless printer you've determine from the above steps, uncheck the box that says "Query the printer and automatically select the driver to use" and click next, leave the following at the default "Standard" and click next, then use the subsequent dialog box to install the driver that you said you have already downloaded using the "Have Disk" button and browsing to the driver location where you downloaded it to. Make sure that you have extracted the driver previously if it was a compressed file or self extracting zip or executeable.
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