(please forgive me for double posting)
Sorry if I didn't write the original properly

. After looking through some other submissions, I didn't include much info as I should have in the above post. So here's as much as I can think of:
Name: KVIrc - K-Visual-IRC Client
Website:
http://www.kvirc.net
Help forum:
http://forum.kvirc.ru/
License: GPL - Slightly modified (see clause 13)
Unicode support
Lastest Version: 3.2.6 (this is the first with a portable option)
Direct Download:
ftp://ftp.kvirc.net/pub/kvirc/snapshots ... 070118.exe
Download size: 6413 KB
Writes no registy entries (to my knowledge) - Just make sure you don't pick it as your default IRC client on first run.
Was programmed in C++
Writes settings to "Settings" and "Downloads" folders inside the main program folder (when configured portably)
Some basic features:
* User interface
o Full GUI Based configuration
o MDI floatable windows
o Built-in help browser
o Themes support (all configurable by GUI or scripting)
o Pseudo-transparency support (up to the desktop on KDE)
o Drag & Drop toolbar editing
o Activity Notifier Pop-Up
o Status bar with Applet support
o Unread text mark
o 14 Languages Translations
* Network
o Proxy support (SOCKv4, SOCKSv5, HTTP)
o Full IPv6 support (also for DCC transfers)
o SSL support (also over IPv6)
o Micryption support
* Core
o Modular architecture: unfrequently used features reside in external modules and are loaded only when necessary
o Extensibility: a huge API for writing extension modules
o UNICODE support
* IRC
o Multiserver connection
o Notify lists (yes, WATCH is supported)
o Ignore lists
o Registered users database
o Lag meter
o Configurable logging
o Standard DCC CHAT and SEND (with resume) support
o Extended DCC types: VOICE, RSEND, GET, RECV
o DCC CHAT over SSL
o DCC bandwidth limit (ability to set it "on the fly")
* Scripting
o Built-in scripting language interpreter
+ scalars, arrays and hashes..
+ aliases
+ popups
+ events
+ scriptable toolbars
+ Perl support
+ Ability to translate scripts (by the means of the tr() function)
+ a lot more
* Objects support in scripting language: yes , now you can do OOP
System Requirements: Couldn't find any
Some notes:
Using a flash drive connected to USB 1.1, it can bit a bit slow, but still usable. This doesn't happen with USB 2. Extracted this is one of the bigest IRC clients I've tried (mine is around 35 MBs configured), but it is very easy to use.
A better guide to setting it up:
If you don't want to extract it and do all the moving, I've fairly sure that if you install it, copy the folder, and uninstall it, their shouldn't be any left over registy entries etc.
If you do want to extract it, here's how:
First open the installer with 7zip (or probably Universal Extractor) and extract all files to a folder of your choise (this can take some time). Secondly delete the $COMMONFILES and $PLUGINSDIR folders. Create two folders called help and themes in the main directory. Now navigate to the $_OUTDIR folder (its best to open a new window for this one). Move the "en" folder to the "help" folder you created and the "silverirc" folder to the "themes" folder you made. Now move the "modules" folder from $_OUTDIR to the "config" folder in the main directory, as well as moving "scriptexamples" into "doc" and "cap" into "modules" (this is the "modules" folder that is in the main directory, not the one you moved into "config"). Now delete $_OUTDIR.
After you've either extracted it or done the installing method, run the program (kvirc.exe) and you will be presented with a welcome wizard. Untick the "Make KVIrc default IRC Client" box and click next. Now select the "All settings in shared program folder (portable)" option and click next. The rest is just user and IRC server settings which don't affect portability.
And that should make you a portable KVIrc.