This is a very common concern before thinking for a siebel upgrade.  As per Anjneya "It does depend on the customization of the older application while doing upgrade.Higher the custom application higher the risk.

Next is CRM !!! A lot of discussion is taking place on CRM comparison.                                                                                                                                                                                                                                                               

Thinking about migrating to new CRM . Here are 10 steps for your business to be up and running with the next best CRM Solution in the market.

This article cover the essential tasks that you must perform to create a simple product and make it visible to users. I was trying to  preapare  a hand note on basic steps involved in simple product creation.Lets see how much it help you.
Creating a Product Record 
You enter products into the Siebel system by creating product records. The product record contains the product name and important information about the product, such as its product line name or part number.

The Siebel application architecture though efficient by its design, there are instances where the custom configuration leads to potential performance pitfalls. Such performance related issues can translate into screens that load slowly or database queries that fail to return the sought-after results. Other times, users must click through a puzzling series of screens – rather than just one or two – to get to the information they need.

Creating an order that is based on a quote allows you to verify the quote to check for any errors.  

Product Administration
We got basic understanding of Product Adminstration in first chapter Siebel Product Administration – An Overview (I)
Chapter 2 – Product in Siebel   [Basic terminolgy in Product Admin]

 Siebel Vertical Competency Practices are specifically made for one domain, They fulfill are desired requirement of specific industry. we have disscued a litlle about the siebel horizontals and Verticals , now we are going to discuss about all verticals in detail. 

CREATING A PROPASAL AND PRESENTION 
Summary

A proposal consist of component and section
For each proposal  create a template
Each template consist of any number of section .
Each section consist of any number of component

Flow
Template
Section
   Sub section
   Component

 Scenario
Creating a account proposal with have section like
Cover lettering
 Step 1
Go to ms word  create new document
 Dear[account name]   go to insert menu and pick the field sub menu
 u find this type of dialog box
fill the appropriate value As defined above.then ok it
now u find error message like this
Error! Reference source not found.
 Step2
Creating a style for this template