macbook to monitor via windows laptop
First off, I suggest just going for the appropriate adapter for your MacBook. If you have a Unibody MacBook Pro, you could use a mini DisplayPort to HDMI converter. If you have a newer Retina MacBook Pro, you can just use a plain old HDMI cable. Older non-unibody MacBooks could use a DVI-to-HDMI converter or cable.


miniDP to HDMI (Monoprice, $6.85 + HDMI cable)
DVI to HDMI (Monoprice, $3.33, doesn't carry audio)
HDMI to HDMI can be found on Monoprice for around $3.00.


If you were looking to save money by not buying more adapters and cables and you're serious about using your MacBook with your TV, just buy the right cables and/or adapters. Sites like Monoprice.com and DX.com offer very inexpensive cables that are of no lesser quality to the ones found in big box stores and at the Apple store.

To do what you're asking, relaying through your PC, would require some sort of screen sharing or remote desktop software (over the network, not over USB) but would be more trouble than it's worth and would likely be unsatisfactory if you wanted to do anything graphics intensive (watching a movie, gaming, etc.).

If you really want to give it a shot, here's what I suggest:


In  your MacBook's System Preferences (since OS X Tiger), you can enable a VNC server. Open System Preferences -> Sharing -> enable "Screen Sharing" or on older  versions of OS X, "Apple Remote Desktop" -> go to "Computer Settings" or "Access Privileges…" -> check off "VNC viewers may control screen with password: " and set a good password.
On your PC, you have to install a VNC client or viewer. Two free clients come to mind, RealVNC and TightVNC. Either should work fine. I tried RealVNC. Download the standalone viewer .exe from their website. Find your MacBook's IP address from your router or the "Network" section in your System Preferences. Open RealVNC, type in the IP address, it will warn you that it's not encrypted, continue, enter the password you specified earlier. You should be connected!
Connect your PC to your TV and simply drag the VNC window over onto the TV or, if you're in mirrored mode, you should be good to go. You may have to adjust the resolution in VNC and on your MacBook to get it fit properly on your TV. I found it very laggy (unusable for text editing) over WiFi in Control Mode, so you may want to try going over Ethernet if possible.


Good luck!