im trying to make a black soul gem, and I have found an altar to use, but I have no soul trap spell. I can buy One, but my mysticim (sp?) is to low (novice) to cast any I have found. If I do buy one, can I still use the effect at the spell crafting altar.

No, if your character is not at apprentice level you cannot cast it.

You could buy a soul trap scroll and cast it.

But the better solution, I think, is to just self train mysticism until you can cast the soul trap spell. You can buy a minor detect life spell (or minor dispel) from Edgar Vautrine at Edgar's Discount Spells in the Imperial City (you can buy them other places too) and then just cast the spell over and over until you get to Apprentice level. Then you can cast the lowest level Soul Trap spell. It doesn't take that long to go from Novice to Apprentice with Mysticism. And the Detect Life spell is also useful.

What Im asking is if I can still make a spell with the effect if I cant cast the soul trap spell.

The answer to this question is no.

thanks for the answer.

So other than loot chests, where can I find soul trap scrolls?

Randomly from merchants and corpses.

It appears there may be one instance of a soul trap scroll being in a predetermined place, but UESP wiki does not specify where. You are welcome to check the reference and see what you think. Read the intro, then click on soul trap in the contents and you'll know as much as I do about it: http://www.uesp.net/wiki/Oblivion:Scrolls

Good luck!