installation - Ubuntu alongside Windows not available, how to install it?

I am trying to install ubuntu alongside but the option is not available and I have no knowledge to shrink partitions / mess us with dual boot etc.

i read somewhere
"I think that you already have 4 primary partitions for Windows 7 (Ubuntu cannot create its partitions because you cannot create more than 4 primary partitions) and so Ubuntu can't show you automatically to install along Windows 7."

now my hd is like this

1- no name 39 MB (oem partition)

2- OS (C:) 80 GB (Boot, Page File, Crash Dump, Primary Partition)

3- Data (D:) 180 GB (Primary Partition

4- Recovery 15 GB (System, Active, Primary Partition)

5- Unallocated 20 GB

What I tried is to create a partition with the unallocated space but there is a pop up windows telling me that the partition will be dynamics and no OS can be installed there, I left it unallocated and from linux is unavailable, plus the option alongside windows is still not available.

can someone explain me step by step how to do the alongside installation without go for the dual boot one?

thanks