Do you happen to have the Windows firewall turned on? I've found that it
interferes with sharing. You shouldn't need it as long as the firewall inside
your LinkSys router is working. The router's firewall shouldn't interfere with
local file sharing.

(Digression: Check your firewall with Steve Gibson's free "Shields Up" test at
<http://grc.com> .)

You shouldn't need any additional Linux packages to connect to a folder on your
Windows machine while sitting in front of your Ubuntu machine. To go the other
way - sitting in front of your Windows machine and opening folders on the Ubuntu
machine - see if you have these Samba packages installed:

libsmbclient
nautilus-share
samba
samba-common
samba-doc
smbclient

Probably overkill. Nautilus-share is for Gnome. I'm not sure what you'd need
for KDE. The "samba-doc" package is documentation.

You may also need to create a Samba login/password. This can be identical to
your usual Ubuntu login/password, but is separately maintained:

sudo smbpasswd -a <username>

It will prompt you for a new password twice (after sudo prompts you for your
password, as usual).