Win XP Pro: No Admin authorization problem

I've got a problem setting up my wireless LAN. My main computer is running Win XP Pro and my secondary computer is running Win 98 SE. My router is a Netgear MR 814 v2 and my antenna is a D-Link USB DWL-1222. My network is established so my secondary computer does have internet access through my primary computer. (BTW, the primary computer has a firewall. Should the secondary computer also have a firewall?)

I didn't install my OS. The person who installed my OS had to create an "Admin" user, and named me "JG" as another user. As the only user, I (JG) have almost all rights. But one thing I cannot do is give my secondary computer permission to share the files that are on my primary computer. On the secondary computer, when I click on Neighborhood Network, I get two choices: JG or entire workgroup. When I click on JG it asks for a password which I do not have. I had assumed the person who set this up would have been smart enough (since he did not give me the password) to have set the password=password, but he didn't. When I click on Entire Workgroup it tells me that //jg does not have permission to access this.

I went into Control Panel -> Adminstrative tools, but did not see anything that could be of immediate help.

Can anybody give me a solution? Do I have to start from scratch and reinstall my OS, or is there an easier solution to this problem. My secondary computer (an old Compaq Presario 7594) has 7.4 GB of total HD space, while my main computer has 140 GB of total HD space. This is why I want ot be able to access my files on my main computer. Burning and carrying CDs back and forth is not very profitable when you have a LAN.

Thanks for your time,

Jeff G