I am in the process of updating the os of my macbook pro and have installed from the snow leopard dvd and did the 10.6.8 combo v1.1 as well and wis to update further but i now cannot get preview so i am concerned about going forward. how to get prev

I am updating the OS on my MacBook Pro from 10.5.8.  I have installed 10.6.8 and the 10.6.8 combo v1.1.  I cannot open my older version of Preview and do not appear to have a newer version which i thought would be on the Snow Leopard dvd.  How can I get the correct version of Preview and is it advisable to upgrade to OS7 andOS8?

It is always installed with whatever new version of OS X is installed or appropriate updates. Since you plan to go forward your choice depends on your model. I would urge you to perform a clean install instead of continuing the upgrade path which may interject incompatibilities.
Upgrading to Yosemite
You can upgrade to Yosemite from Lion or directly from Snow Leopard. Yosemite can be downloaded from the Mac App Store for FREE.
Upgrading to Yosemite
To upgrade to Yosemite you must have Snow Leopard 10.6.8 or Lion installed. Download Yosemite from the App Store. Sign in using your Apple ID. Yosemite is free. The file is quite large, over 5 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.
    OS X Mavericks/Yosemite - System Requirements
      Macs that can be upgraded to OS X Yosemite
         1. iMac (Mid 2007 or newer) - Model Identifier 7,1 or later
         2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) - Model Identifier 5,1 or later
         3. MacBook Pro (Mid/Late 2007 or newer) - Model Identifier 3,1 or later
         4. MacBook Air (Late 2008 or newer) - Model Identifier 2,1 or later
         5. Mac mini (Early 2009 or newer) - Model Identifier 3,1 or later
         6. Mac Pro (Early 2008 or newer) - Model Identifier 3,1 or later
         7. Xserve (Early 2009) - Model Identifier 3,1 or later
To find the model identifier open System Profiler in the Utilities folder. It's displayed in the panel on the right.
     Are my applications compatible?
         See App Compatibility Table - RoaringApps.
Upgrading to Lion
If your computer does not meet the requirements to install Yosemite, it may still meet the requirements to install Lion.
You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax.  It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.
     Lion System Requirements
       1. Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7,
           or Xeon processor
       2. 2GB of memory
       3. OS X v10.6.6 or later (v10.6.8 recommended)
       4. 7GB of available space
       5. Some features require an Apple ID; terms apply.
Before attempting a clean install you want to first download the appropriate installer application from the App Store. It will download into your Applications folder. You need to make a copy of it in your Downloads folder so you can make a bootable USB flash drive:
Make Your Own Mavericks, Mountain/Lion Installer
After downloading the installer you must first save the Install Mac OS X application. After the installer downloads DO NOT click on the Install button. Go to your Applications folder and make a copy of the installer. Move the copy into your Downloads folder. Now you can click on the Install button. You must do this because the installer deletes itself automatically when it finishes installing.
   2. Get a USB flash drive that is at least 8 GBs. Prep this flash drive as follows:
Open Disk Utility in your Utilities folder.
After DU loads select your flash drive (this is the entry with the mfgr.'s ID and size) from the leftside list. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, set the partition scheme to GUID then click on the OK button. Click on the Partition button and wait until the process has completed.
Select the volume you just created (this is the sub-entry under the drive entry) from the left side list.
Click on the Erase tab in the DU main window.
Set the format type to Mac OS Extended (Journaled.) Click on the Options button, check the button for Zero Data and click on OK to return to the Erase window.
Click on the Erase button. The format process can take up to an hour depending upon the flash drive size.
Use DiskMaker X to put your installer clone onto the USB flash drive.
Make your own Yosemite flash drive installer using the Yosemite tool:
You can also create a Yosemite flash drive installer via the Terminal. Yosemite has its own built-in installer maker you use via the Terminal:
How to Make an OS X Yosemite Boot Installer USB Drive