You can deploy various files like .jpg, gif, css, javascript etc along with
your WebPart solution package using <Templatefiles< tag, avilable in your
solution's manifest.xml file.
You however, do not modify the
<TemplatesFile> tag directly, instead you would mimic the 12 hive folder
structure in your webpart and will add the files that you want to deploy under
the structure. The Template files tag in manifest file will automatically be
created by Vsewss once you build the solution. See the detailed example below.
Please Note : If you want to create a solution package for just
deploying some files in 12 hive, for e.g. deploying custom aspx page or layouts
page or Custom css or javascript file then see the Related Post Deploy Custom Css file in SharePoint 2007 with Solution Package
Below are the Steps
to deploy some additional files in SharePoint's 12 hive with your webpart
solution package. Also, note that the WebPart used in the below example was
created using WebPart template available with VSeWSS.
Step 1: Create the Template Directory structure
in your webpart Project. For e.g to deploy your css or Image files in 12 hive's
STYLES library, Create a folder structure as
Templates->LAYOUTS->1033->STYLES->Your custom Folder. Now, add
your files under your Custom Folder.
See the screen below 
Step 2: Build the WebPart.
Now, open manifest.xml and look
at the tag <TemplateFiles>. You will
notice that VSeWSS has added entries for all the files in your custom folder as
TemplateFiles. This defines the Path where these files will be deployed. See the
Image below. 
Step 3: Now, deploy the Solution.
Step 4 : Verify that the
Folder "MyCustomWebPart"(your custom folder name) is available in the Styles
folder.
If you want to use the deployed Images in your WebPart, you can
simply use it with below url
_LAYOUTS\1033\STYLES\MyCustomWebPart\blahblah.jpg."
For details on
how to register and use Css and Javascript files in your webpart,see the post
Using External Javascript, CSS or Image File in a WebPart of SharePoint
Below Code is to ensure that your webpart gets removed
from WebPart gallery during retraction. This is done by adding a Feature receiver in your
webpart solution file.
Step 4: Create a FeatureReceiver.cs class
file. Add the below code for feature deactivating.
public override void
FeatureDeactivating(SPFeatureReceiverProperties properties)
{
SPSite
site = null;
try
{
site = properties.Feature.Parent as SPSite;
using (SPWeb web = site.RootWeb)
{
SPList list = web.Lists["Web Part
Gallery"];
// go through the items in reverse
int count =
Convert.ToInt32(list.ItemCount);
for(int i = count -1 ;i>= 0; i--)
{
// format name to look like a feature name
string webpartName
= list.Items[i].Name;
webpartName = webpartName.Substring(0,
webpartName.IndexOf('.'));
// delete web parts that have been added
if (properties.Feature.Definition.DisplayName == webpartName)
{
list.Items[i].Delete();
break;
}
}
}
}
finally
{
if (site != null)
site.Dispose();
}
}
A Detailed article is Here
.
Now, add an entry for Feature receiver in your feature.xml.
Specify the ReceiverAssembly and the receiver class. Build the Project. see fig
below : 
Step 4 : Retract the solution from central Admin -> operations
-> solution managment.
Verify that the Custom folder in STYLES library is
removed.
Note : If you custom folder with Images is deployed in
Templates->LAYOUTS->1033->IMAGES folder,It wont get removed on
retracting the solution. The Images which are deployed directly in the
Templates->LAYOUTS->1033->IMAGES folder gets retracted. For more on
Template files and other options in manifest.xml please see wsp
Schema