First see this link to decide which approach you want for migration
if you are using inplace migration approach then go through this link
Install and configure SharePoint 2010, on a new environment
Determine hardware and software requirements (SharePoint Server 2010)
Planning Logical architecture components
deployment guide for Microsoft SharePoint Server 2010
After installing and configuring your new SharePoint 2010,
Moving Content Database from SP 2007 to SP 2010
1) Find the content Database; These are listed under Central Admin->Application Management->Site Collection List
2) Backup the content database, You could alternatively detach it, and copy it. Just doing a backup in SQL Server Management studio is easier.
3) Restore content database to new server, Copy the BAK file to new server. Create an empty DB in Management Studio, restore from backup, you may
need to change an option in the "options" tab of the restore dialog to get it to work. (Overwrite db).
4) Create Web App on SharePoint 2010
5) Remove Content Database from the new web app.
Now use STSADM to add restored DB to this web app
c:\program files\common files\microsoft shared\web server extentions\14\bin on new server is where you can find the STSADM.
run this command from there. Which will upgrade the content db to 2010?
stsadm -o addcontentdb -url http://yourwebapp:port -databasename yourcontentdb -databaseserver yoursqlserver
6) Run ISSRESET from command prompt
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