Windows 7/2008 currently comes with downloadable installer, but usage is limited to test purposes for 90-days.
However, there are options to extend this period. Use administrator privileged shell all the time to do this (start menu/run/cmd/right click - run as administrator)
Query current windows version:
winver
Temporary official way to extend period:
Reinstall license:
Run a command line as administrator, and execute the following:
slmgr.vbs /rilc
Extend evaluation period with 30 days. You can use this 3 times max:
slmgr.vbs /rearm
If you're done with this 3 extensions, you can still extend the period by setting the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform
set SkipRearm to 1.
Now you can use the rearm 8 times (30 days each):
slmgr.vbs /rearm
Not-official way to do so...don't blame me if something goes wrong. This will disable the genuine check and will allow updates as well:
net stop sppsvc
locate C:\windows\system32\slui.exe
Change owner to administrator
Give administrator full control
rename to __slui.exe
Do the same with
C:\windows\system32\en-US\slui.exe.mui
net start sppsvc