There is a really easy guide right here:
Basic steps are:
1. Copy over Hotmail emails to Gmail
2. Copying your contacts over (remember that they will not synchronise, so you will need to 'add' new people to Gmail as well unfortunately :(
3. Allow using your Hotmail email address when sending from Gmail ("Add another email address")
4. Redirect new Hotmail to Gmail *****
This is the tricky bit. I find that if you setup using your Gmail at this page [https://accountservices.passport.net/PPNetworkHome.srf?lc=1033] then you can link Hotmail-Gmail using Linked ID's, and it's "more likely" that Hotmail will let you redirect to a non-MSN email. Otherwise you will need Easy Email Forwarding (Windows Forwarding client) and FreePops (I have copies if people want them) or GetMail (old version of EEF), or IzyMail (Web service, but want money).