Severe Sub-Domain re-direction Issues..

[SaN-DeeP]

I am running couple of sub-domains via our main domain: http://www.techarena.in
Sub-domains in use:
http://forums.techarena.in
http://gallery.techarena.in
Here are the contents of my current .htaacess file placed on http://www.techarena.in:

ErrorDocument 400 /
ErrorDocument 401 /
ErrorDocument 403 /
ErrorDocument 404 /
#
Options +Indexes +FollowSymlinks
RewriteEngine on
RewriteBase /
#
# Prevent duplicate content on gallery and forums subdomain
RewriteCond %{HTTP_HOST} ^(gallery|forums)\.techarena.in
RewriteRule ^(gallery|forums)/[^.]+$ - [F]
#
[COLOR=Red]# Redirect gallery and forums subdirectories to subdomains
RewriteCond %{HTTP_HOST} ^www\.techarena\.in
RewriteRule ^gallery/([^.]+)$ http://gallery.techarena.in/$1/ [R=301,L]
RewriteCond %{HTTP_HOST} ^www\.techarena\.in
RewriteRule ^forums/([^.]+)$ http://forums.techarena.in/$1/ [R=301,L][/COLOR]
#
RewriteCond %{HTTP_HOST} ^202\.54\.145\.178 [OR]
RewriteCond %{HTTP_HOST} ^techarena\.in
RewriteRule (.*) http://www.techarena.in/$1 [R=permanent,L]

My Problems:
1.
Serps + Guests are able to get to my sub-domains from following URLs as well:
www.techarena.in/forums/forumdisplay.php?f=18
http://forums.techarena.in/forumdisplay.php?f=18

This is creating lot of dupe content, i want to fix this problem, with a 301/permanent re-direct (without loosing any rankings or getting penalties)

2.
I am running a Vbulletin forum software script, any user typing a wrong URL or trying to access any improper location should to be re-directed to the folder root appropriately, cause I lost lot of pages from my forums and main site due to a recent db crash.
I want to achieve following if a user tries to access:

forums.mydomain.in/showthread.php?t=XXXXX which does not exists (reason got deleted)
should be re-directed properly to forums.mydomain.in

3.
There are many pages indexed in Google and Yahoo via our Site IP Address as well for example:
000.000.000.000/forums/somepage
I want to re-direct such pages to forums.mydomain.in/somepage

4. While trying to re-direct users from 404 URLs on forum, entire .CSS and image paths appear to be invalid, is there a possible solution for re-directing users from 404 pages to root properly?

(Note: Only the code marked in red in above .htaccess file wont work, can some confirm if rest of things are done properly ?)

Need help to fix above problems: