steel

Seeing as their rules are identical, why not choose the models you like best?

 Personally, I'm a fan of the Vostroyans.

I have the steel legion codex so I may start that army but I have heard poeple say that mechanised infantry are weak against heavy armored units like necrons, tau, or chaos. So could any one suggest an army list but it must included commisar yarrick

Steel Legion Codex? I think you are a bit behind in terms of rules edition. There's now only the Imperial Guard Codex. There are no separate books for different guard units.

Yup...there is no official Steel Legion codex in this current edition. 

Just buy the newest IG codex.  Pretty much every IG legion is the same, but you can get special cahracters to change things up a bit.  In other words, you can still play Steel Legion...even as a non-mechanized company.

well it is not a codex dedacated to steel legion but it the armaggedon codex and it covers a lot of the special rules for the steel legion and armaggedon history

Yup...WAY outdated codex.  I think there have been two new IG codexes since that came out.

Get the new one...FAR superior to that one.  And again, you can still play Steel Legion...with BETTER rules.

Well I want to have a massive battle battle in Warhammer world on the cathedral board using the special rules of each force either salamanders, black templars, ork speed freek, or armageddon steel legion.

conversion

<Well I want to have a massive battle battle in Warhammer world on the cathedral board using the special rules of each force either salamanders, black templars, ork speed freek, or armageddon steel legion.>

And this is perfectly possible with the new codexes.  The new codexes have pretty much every special rule in those old codexes PLUS COOL NEW ONES!  

For example, you want Salamanders?  Just take a standard space marine army, add the special character Vulkan He'stan and suddenly ALL thunder hammers count as master-crafted, and ALL flamers, meltaguns, multimeltas, etc count as twin-linked!!!  They weren't NEARLY that cool in that old codex.

The problem with using the old codexes is the rules have changed ALOT since that edition.  Any army you made with those rules will be illegal to play according to the new rules (and I doubt you'll find anyone who still uses the old rules).

Tell you what, tell me the special rules for Steel legion and I can easily tell you how to make a SL army with the new codex.