Advertisement Link Every X Post? VB 2.3.x

[interlution]

I'd like to put a simple text ad every 3rd post (or 5 or 10 etc.) on my forums. I've tried various <if condition> variations in my postbit:

<if condition="$post[postcount] % 3 == 0">
Advertisement
</if>

Results in all the posts having the ad.

if I do:

<if condition="$post['postcount'] % 3 == 0">
Advertisement
</if>

I get "Parse error: parse error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRING or T_VARIABLE or T_NUM_STRING functions.php(374) : eval()'d code on line 39" errors.

Is the <if condition> only for VB3?

Among other hacks, I've installed this post counter: https://vborg.vbsupport.ru/showthrea...threadid=22083

Sorry if this is a newbie question. I've tried my best to search around vbulletin.org, vbulletin.com and vbulletintemplates.com for a few hours and I can't figure this out.

BTW, I love this new vbulletin.org site layout! It's the best looking VB3 board I've seen.